The 50 most-cited articles in The Analyst, 2019

Fast-scan cyclic voltammetry (FSCV) is used with carbon-fiber microelectrodes for the real-time detection of neurotransmitters on the subsecond time scale. With FSCV, the potential is ramped up from a holding potential to a switching potential and back, usually at a 400 V s-1 scan rate and a frequency of 10 Hz. The plot of current vs. applied potential, the cyclic voltammogram (CV), has a very different shape for FSCV than for traditional cyclic voltammetry collected at scan rates which are 1000-fold slower. Here, we explore the theory of FSCV, with a focus on dopamine detection. First, we examine the shape of the CVs. Background currents, which are 100-fold higher than faradaic currents, are subtracted out. Peak separation is primarily due to slow electron transfer kinetics, while the symmetrical peak shape is due to exhaustive electrolysis of all the adsorbed neurotransmitters. Second, we explain the origins of the dopamine waveform, and the factors that limit the holding potential (oxygen reduction), switching potential (water oxidation), scan rate (electrode instability), and…

Electrochemical biosensors have been applied in a broad range of clinical applications for pathogen biomarker detection and medical applications and diagnosis due to the sensitivity of electrochemical methods and the bioselectivity of the components. The complexity of clinical conditions with various biofoulants (proteins, cells, polysaccharides and lipids) severely influences the reliability and stability of sensors for direct detection or immersion under changing conditions. Therefore, designing an antifouling sensing platform that can effectively reduce undesired binding to maintain biosensor performance in optimized analysis is necessary. For this purpose, the fundamental mechanisms of fouling materials and commonly used biocompatible antifouling components have been discussed, and the relevant effective modification strategies are introduced in this review. Recent advances in these strategies are demonstrated in examples with analysis of essential modification methods for reliable sensing in non-specific binding solutions or complex biofluids. The challenges and future…

Anodic Stripping Voltammetry (ASV) has the capability to detect heavy metals at sub ppb-level with portable and cheap instrumentation making it ideal for in the field (at the source) analysis, however, commercial activity is surprisingly limited. The more commonly used liquid mercury electrodes are now obsolete due to toxicity concerns, and replacements are all based around solid electrodes, which come with their own challenges. This tutorial review aims to discuss the experimental practicalities of ASV, providing a clear overview of the issues for consideration, which can serve as a guide for anyone wanting to undertake analytical ASV. Choice of electrode material (with or without subsequent modification) and solution composition (pH, electrolyte, buffer) are important parameters, as well as an understanding of pH dependent metal speciation and possible intermetallic effects. Measurements made on model solutions often differ from those made on environmental samples with the latter containing organic matter, biological and inorganic species, which themselves can adsorb metal ions.…

This paper reports the comparison of the electrochemical properties of 3D PLA-graphene electrodes (PLA-G) under different activation conditions and through different processes. In this work, the performance of the electrodes was evaluated after polishing, electrochemical and chemical treatments and a combination of them. The best results were obtained with hydroxide activation using 1.0 mol L-1 NaOH for 30 min of immersion, which promoted the saponification of PLA exposing the graphene nanoribbon structures. The improvement was more evident also after electrochemical activation, which led to a great increase in surface area, defects, electron transfer rate and amount of edge sites. The analytical performance of the proposed PLA-GNaOH-30-EC electrode was evaluated in the presence of dopamine (DA) by three electrochemical techniques, presenting a broad linear range, and limits of detection of 3.49, 2.17 and 1.67 μmol L-1 were obtained by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), respectively. The separation and quantification of…

Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes (CFMEs) is a versatile electrochemical technique to probe neurochemical dynamics in vivo. Progress in FSCV methodology continues to address analytical challenges arising from biological needs to measure low concentrations of neurotransmitters at specific sites. This review summarizes recent advances in FSCV method development in three areas: (1) waveform optimization, (2) electrode development, and (3) data analysis. First, FSCV waveform parameters such as holding potential, switching potential, and scan rate have been optimized to monitor new neurochemicals. The new waveform shapes introduce better selectivity toward specific molecules such as serotonin, histamine, hydrogen peroxide, octopamine, adenosine, guanosine, and neuropeptides. Second, CFMEs have been modified with nanomaterials such as carbon nanotubes or replaced with conducting polymers to enhance sensitivity, selectivity, and antifouling properties. Different geometries can be obtained by 3D-printing, manufacturing arrays, or fabricating carbon…

Raman spectroscopy is widely used as a fingerprint technique for molecular identification. However, Raman spectra contain molecular information from multiple components and interferences from noise and instrumentation. Thus, component identification using Raman spectra is still challenging, especially for mixtures. In this study, a novel approach entitled deep learning-based component identification (DeepCID) was proposed to solve this problem. Convolution neural network (CNN) models were established to predict the presence of components in mixtures. Comparative studies showed that DeepCID could learn spectral features and identify components in both simulated and real Raman spectral datasets of mixtures with higher accuracy and significantly lower false positive rates. In addition, DeepCID showed better sensitivity when compared with the logistic regression (LR) with L1-regularization, k-nearest neighbor (kNN), random forest (RF) and back propagation artificial neural network (BP-ANN) models for ternary mixture spectral datasets. In conclusion, DeepCID is a promising method for…

Microbial infections remain the principal cause for high morbidity and mortality rates. While approximately 1400 human pathogens have been recognized, the majority of healthcare-associated infectious diseases are caused by only a few opportunistic pathogens (e.g., Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli), which are associated with increased antibiotic and antimicrobial resistance. Rapid detection, reliable identification and real-time monitoring of these pathogens remain not only a scientific problem but also a practical challenge of vast importance, especially in tailoring effective treatment strategies. Although the development of vaccinations and antibacterial drug treatments are the leading research, progress, and implementation of early warning, quantitative systems indicative of confirming pathogen presence are necessary. Over the years, various approaches, such as conventional culturing, straining, molecular methods (e.g., polymerase chain reaction and immunological assays), microscopy-based and mass spectrometry techniques, have been employed to…

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are…

Antibiotics have been noted as an important class of emerging contaminants in the environment. Metal-organic frameworks (MOFs), which have been intensely investigated as a novel kind of sensing material, have been tentatively applied to the detection of antibiotics in recent years. In this work, a nanoscale MOF (In-sbdc) with a strong (quantum yield = 13%) and stable emission in water was synthesized. With its effective spectral overlap with tetracyclines, adsorption preconcentration and the usage of a masking agent, In-sbdc gave sensitive responses to a series of tetracycline antibiotics (tetracycline, chlorotetracycline and oxytetracycline) with detection limits of 0.28-0.30 μM, but another eight tested kinds of antibiotics did not cause a remarkable change in its emission (<10% of the response caused by an equal amount of tetracyclines). This MOF-based sensing system was successfully applied to tetracyclines detection in a series of actual water and food samples.

As a series of important metal materials, rare earth elements and their related derivative compounds have received significant attention because of their narrow emission bands, noncytotoxicity, excitation of multiple fluorescence colors and electrochemical properties. These unique properties endow rare earth-based nanomaterials with great potential for application in various fields such as in supercapacitors, batteries, sensors, devices and solar cells. This review presents a general description of the electrochemical properties of rare earth-based nanomaterials. The developments and improvements of their electrochemical applications in electrochemical sensors for the detection of small biomolecules and DNA, supercapacitors, batteries and electrochemical catalysis towards the hydrogen evolution reaction have also been discussed.

Correction for 'A new point-of-care test for the diagnosis of infectious diseases based on multiplex lateral flow immunoassays' by Hanbi Kim et al., Analyst, 2019, 144, 2460-2466.

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy has been used widely for probing the molecular properties of materials. Coupling a synchrotron infrared (IR) beam to an ATR element using a high numerical aperture (NA) microscope objective enhances the spatial resolution, relative to transmission or transflectance microspectroscopy, by a factor proportional to the refractive index (n) of the ATR element. This work presents the development of the synchrotron macro ATR-FTIR microspectroscopy at Australian Synchrotron Infrared Microspectroscopy (IRM) Beamline, and demonstrates that high quality FTIR chemical maps of single cells and tissues can be achieved at an enhanced spatial resolution. The so-called "hybrid" macro ATR-FTIR device was developed by modifying the cantilever arm of a standard Bruker macro ATR-FTIR unit to accept germanium (Ge) ATR elements with different facet sizes (i.e. 1 mm, 250 μm and 100 μm in diameter) suitable for different types of sample surfaces. We demonstrated the capability of the technique for high-resolution single cell…

Herein, the CuO/ZnO@Fe3O4-carbon nanotubes (CNTs)-nanocomposite (NC), as a sorbent for magnetic dispersive micro-solid phase extraction, was developed for the determination of chlorogenic acid (CGA) in the medical extract of plants, food, and water samples in combination with high-performance liquid chromatography. The CuO/ZnO@Fe3O4-CNTs-NC was characterized by FESEM, EDS, XRD, TEM, BET, FT-IR, and VSM. Significant parameters (pH, temperature, eluent volume, vortex time, sonication time, CuO/ZnO@Fe3O4-CNTs-NC mass, and desorption time) that affected the extraction efficiency of CGA were optimized using Plackett-Burman as the screening design and the central composite design as the optimization strategy. Under the optimized conditions, the analytical parameters were obtained. The optimized method showed good linearity and a linear regression coefficient >0.9893. The enrichment factors ranged from 102.43 to 123.76 with the preconcentration factor of 60.0. The limits of detection (LOD) and the limits of quantification (LOQ) were 0.034-0.061 ng mL-1 and 0.114-0.202 ng mL-1,…

Carbon dots (CDs) have broad prospective applications in various fields, and expanding the applications of fluorescent CDs, especially for CDs derived from bacteria, is a major research goal. In this study, novel CDs derived from Escherichia coli BW25113 (WT) were successfully synthesized via a one-step hydrothermal method. Unlike previously developed CDs-E. coli, CDs-WT can be used for microbial imaging of both live and dead cells. We demonstrated the biocompatibility, excellent penetrability, and nontoxic characteristics of CDs-WT for use as fluorescent probes for bioimaging both in vitro and in vivo. Importantly, we provide the first demonstration of CDs-WT distribution in various organs of mice, including the ability to cross the blood-brain barrier and the potential for rapid excretion through the intestines. Additionally, CDs-WT can be instantly utilized as a fluorescent probe for the highly selective and rapid detection of p-nitrophenol (p-NP) by the inner filter effect, with a limit of detection for p-NP of 11 nM, the lowest value reported to date. Hence, our results…

Recently, the pollution and damage caused by antibiotics in water have aroused serious concerns. In this situation, it is extremely important to develop a highly effective approach to detect antibiotics in water. In this contribution, we built a Cd-MOF material with stable fluorescence properties, using bbi = 1,4-bis(2-methyl-imidazol-1-yl)butane and H2L = 1,2-phenylenediacetic acid as organic ligands and Cd(NO3)2·4H2O as the metal node. The highly selective response of this MOF probe to ceftriaxone sodium (an antibiotic) can reach up to the ppb level in water, along with a fast response time, acid and alkali resistance, and anti-interference ability.

Insulin is an important polypeptide hormone that regulates carbohydrate metabolism. Abnormal levels of insulin are associated with diabetes mellitus that is characterized by chronic hyperglycemia. Therefore, reliable quantification of insulin is important for clinical purposes such as the diagnosis and treatment of diabetes. Nowadays, immunoassays and chromatographic assays are the primary methods that have been developed for insulin analysis. In this review, we have summarized the principles, sensitivity, linearity range, and recovery as well as the advantages and limitations of the most prevalent methods. Generally, immunoassays including enzyme-linked immunosorbent assay (ELISA), chemiluminescence immunoassay (CLIA), radioimmunoassay (RIA) and on-chip immunoassay show good selectivity towards insulin with less interferences and high throughput. Chromatographic assays including high performance liquid chromatography coupled with ultraviolet detection (HPLC-UV), micellar electrokinetic capillary chromatography (MECC), and liquid chromatography with tandem mass spectrometry…

with carbon nanotubes or beta-cyclodextrin may improve the sensing performance. Another key challenge in the research is to develop relationships between glutamate and biofluids. Finally, we have to advance electrochemical sensors that are compatible to detect glutamate in physiological conditions for long durations of time.

MicroRNA (MiRNA) plays a crucial role in biological cells to enable assessment of a cancer's development stage. Increasing evidence has shown that the accurate and sensitive detection of miRNA holds the key toward correct disease diagnosis. However, some characteristics of miRNAs, such as their short chains, low concentration, and similar sequences, make it difficult to detect miRNA in biological samples. Nanomaterials usually have good optical, electronic, and mechanical properties and therefore provide new possibilities for improving the performance of miRNA assays. Many different sorts of nanomaterials, including metal nanomaterials, carbon nanomaterials, quantum dots, and transition-metal dichalcogenides, have been used to construct optical and electrochemical assays for miRNA and have shown attractive results. This review describes recent efforts in the application of nanomaterials as sensing elements in electrochemical and optical miRNA assays. The analytical figures of merit of various methods for the detection of miRNA are compared in the present article. The current…

p-Nitrophenol (p-NP) pollutants are widely present in soil and aquatic environments and can seriously impair the health of living beings. Hence, a rapid, sensitive, and selective method for p-NP detection is urgently needed. Herein, for the first time, we successfully synthesized fluorescent carbon dots (CDs) from Bacillus cereus (BC) via a one-step hydrothermal process. The obtained CDs-BC can be applied as a rapid, highly selective, and sensitive sensor for p-NP detection. The fluorescence quenching efficiency of the CD-BC sensor exhibited excellent linear responses with p-NP concentrations at both 0.3-6.5 μM and 6.5-30 μM, with a detection limit of 0.11 μM. The mechanism of p-NP detection is based on the inner filter effect (IFE). Preliminary bacteria, cell, and animal studies showed that the as-prepared CDs-BC possess high photostability, excellent biocompatibility, low or no biotoxicity, and multicolor fluorescence emission properties; furthermore, they can be rapidly excreted from the body of mice, which suggests their potential for applications in the biomedical field.

Biomarkers are unquestionable biological indicators for diagnosis and therapeutic interventions providing appropriate classification of a wide range of health disorders and risk factors. Nonetheless, the detection and quantification of biomarkers need to be tested with sufficient reliability by robust analytical methods in order to assure clinical performance in health care settings. Since the analytical performance is determined by the sensitivity and specificity of the method employed, techniques have been intensively refined in order to avoid the misinterpretation of results and undesirable bias. Although biomarkers can be detected with the existing analytical techniques, to reproducibly quantify them in decentralized settings or remote locations with the required accuracy is still a challenge. Currently, only a few point-of-care devices for biomarker evaluation are commercially available. Thus, more focused research efforts are needed to overcome these limitations in order to provide universal patient-centered care platforms. To this end, plasmonic biosensors can be conveniently…

EVs/exosomes are considered as the next generation of biomarkers, including for liquid biopsies. Consequently, the quantification of EVs/exosomes is crucial for facilitating EV/exosome research and applications. Paper-based enzyme-linked immunosorbent assay (p-ELISA) is a portable diagnostic system with low cost that is simple and easy to use; however, it shows low sensitivity and linearity. In this study, we develop p-ELISA for targeting EVs/exosomes by using streptavidin agarose resin-based immobilization (SARBI). This method reduces assay preparation times, provides strong binding, and retains good sensitivity and linearity. The time required for the total assay, including preparation steps and surface immobilization, was shortened to ∼2 h. We evaluated SARBI p-ELISA systems with/without CD63 capture Ab and then with fetal bovine serum (FBS) and EVs/exosome-depleted fetal bovine serum (dFBS). The results provide evidence supporting the selective capture ability of SARBI p-ELISA. We obtain semiquantitative p-ELISA results using an exosome standard (ES) and human serum (HS), with…

In this study, a 4-aminobenzenethiol-functionalized core-shell silver-coated gold nanoparticle (Au@Ag-4ABT NP) system was designed for the rapid sensing of carbendazim (CBZ) using a combination of naked-eye colorimetry and surface-enhanced Raman spectroscopy (SERS) dual-channel approach. Under alkaline conditions, the deprotonated CBZ species could interact with Ag surfaces via the N-Ag-O and N-Ag-N bonds. As a result, the neighboring Au@Ag-4ABT NPs would come closer through π-π interactions inducing the aggregation of Au@Ag-4ABT NPs. The aggregation of nanoparticles caused changes in the optical properties of the colloidal system, allowing observation with naked eyes, while the generation of more localized surface plasmon resonance "hotspots" between the adjacent Au@Ag nanoparticles permitted monitoring by the SERS technique. The proposed method showed effective sensitivity toward CBZ with limit of detection and limit of quantitation values of 37 and 122 ppb, respectively. In addition, the proposed dual-channel assay could serve as a simple and rapid method for sensing CBZ in tap…

for PSA, CEA, and AFP, respectively, suggesting that this approach can be a good candidate in point of care testing (POCT) for rapid and sensitive biomarker detection and has a huge potential in multiplex analysis and cancer diagnosis.

, respectively. The reproducibility and repeatability (RSDs, n = 5) were in the range of 3.65-8.66% and 1.84-5.54%, respectively. Overall, the proposed method was successfully used to determine CA in the medical extracts of plants and water samples with favorable recoveries.

Ion mobility-based separation prior to mass spectrometry has become an invaluable tool in the structural elucidation of gas-phase ions and in the characterization of complex mixtures. Application of ion mobility to structural studies requires an accurate methodology to bridge theoretical modelling of chemical structure with experimental determination of an ion's collision cross section (CCS). Herein, we present a refined methodology for calculating ion CCS using parallel computing architectures that makes use of atom specific parameters, which we have called MobCal-MPI. Tuning of ion-nitrogen van der Waals potentials on a diverse calibration set of 162 molecules returned a RMSE of 2.60% in CCS calculations of molecules containing the elements C, H, O, N, F, P, S, Cl, Br, and I. External validation of the ion-nitrogen potential was performed on an additional 50 compounds not present in the validation set, returning a RMSE of 2.31% for the CCSs of these compounds. Owing to the use of parameters from the MMFF94 forcefield, the calibration of the van der Waals potential can be extended…

Thermogravimetric analysis (TGA) coupled with evolved gas analysis-FT-IR has been examined as a potential method to study the functional group content for surface modified silica nanoparticles. A comparison with a quantitative solution NMR method based on analysis of groups released after dissolution of the silica matrix is used to provide benchmark data for comparison and to assess the utility and limitations of TGA. This study focused primarily on commercially available silicas and tested whether it was possible to use a correction based on bare silica to account for the significant mass loss that occurs due to condensation of surface hydroxyl groups and loss of matrix-entrapped components at temperatures above ∼200 °C. Although this approach has been used successfully in the literature for in-house prepared samples, it was problematic for commercial silicas prepared by the Stöber method. For these materials the agreement between estimates from qNMR and TGA mass loss was poor in many cases. However much better agreement was observed for samples for which the mass loss above 200 °C…

In this work, a complex dielectric transformation of UV-vis diffuse reflectance spectra is proposed to estimate the optical band-gap energies of an array of materials classified as semi-conductors, conductors and insulators and the results are compared with the more common Kubelka-Munk (K-M) transformation. The results show a close match between the proposed method and the Tauc model based on the K-M transformation within ca. 0.16-7.07% variation. The proposed method based on the well-established dielectric transformation is unique in a way to estimate band-gap energy when there remain unresolved or multiple absorption peaks in the diffuse reflectance spectra. Importantly, the complex dielectric transformation method also distinguishes the class of the materials which is of paramount importance to validate and substantiate the band-gap energy values.

Fluorescence detection of pesticide contamination enables timely control of food safety. This study aims to construct novel and facile microfluidic paper-based analytical devices for the ratiometric fluorescence determination of pesticides. Through fluorescence resonance energy transfer (FRET) of nitrobenzoxadiazole (NBD) and CdTe quantum dots (QDs), the new microfluidic paper chips allowed the rapid and selective visual detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The performance changes of the fluorescent material on solid matrix material were studied in detail. The sensor products exhibited visual observability and fluorescence characteristics. Under optimized conditions, the sensors showed satisfactory linearity in the range of 0.56-80 μM, and achieved detection limits as low as 90 nM. The sensors were successfully applied for soybean sprouts and lake water samples. Four levels of spiked-in 2,4-D concentrations were obtained with high recovery rates ranging from 86.2% to 109.5% and the RSD less than 4.19%. Thus, the present work described the integration of surface…

Porous graphitized carbon (PGC) based chromatography achieves high-resolution separation of glycan structures released from glycoproteins. This approach is especially valuable when resolving structurally similar isomers and for discovery of novel and/or sample-specific glycan structures. However, the implementation of PGC-based separations in glycomics studies has been limited because system-independent retention values have not been established to normalize technical variation. To address this limitation, this study combined the use of hydrolyzed dextran as an internal standard and Skyline software for post-acquisition normalization to reduce retention time and peak area technical variation in PGC-based glycan analyses. This approach allowed assignment of system-independent retention values that are applicable to typical PGC-based glycan separations and supported the construction of a library containing >300 PGC-separated glycan structures with normalized glucose unit (GU) retention values. To enable the automation of this normalization method, a spectral MS/MS library was…

Raman spectroscopy has been employed for studying the hydrogen bonding states of water molecules for decades, however, Raman imaging data contain thousands of spectra, making it challenging to obtain information on water with different hydrogen bonds. In the current study, a novel method combining confocal Raman microscopy (CRM) imaging with the iterative curve fitting algorithms was developed to determine the distribution of water contents at the cellular level and water states with different hydrogen bonds in apple tissues. Raman imaging data ranging from 2700 to 3800 cm-1 were acquired from whole cells in the apple tissue, which were then decomposed into seven sub-peaks using the fixed-position Gaussian iterative curve fitting (FPGICF) algorithm. The content and hydrogen bonding states of cellular water were calculated as the area sum of the OH stretching vibration and the area ratio of DA-OH over DDAA-OH stretching vibration or the number of hydrogen bonds of each water molecule, respectively. Finally, the area of each sub-peak, the area sum of the OH stretching vibration, and…

A new class of functional materials, carbon nitrides, has recently attracted the attention of researchers. Carbon nitride is a metal-free carbonaceous material, possessing a high N : C ratio with structure ranging from polymeric to graphitic form, constituting heptazine or triazine rings as structural motifs. It entered into the frame as a heterogeneous photocatalyst owing to its medium band gap, porosity, and high thermal and chemical inertness. Intensive research aimed towards exploring its inherent potentials has opened up a new area of study in the field of sensors; moreover, due to tunability of its electronic and optical properties, high stability, biocompatibility and low cost, it can be used in the area of sensing. In this review, we highlighted various strategies for the development of nanoscale morphological varieties of carbon nitrides and fabrication of sensors based on the luminescence properties of the carbon nitride materials. Herein, we exclusively envisioned new vistas for carbon nitrides as an imperative candidate for the fabrication of ideal sensors.

We herein report a facile approach for the preparation of horseradish peroxidase (HRP)-mimic glucose oxidase-conjugated graphene oxide/MnO2 (GOD-GO/MnO2) as new nanozyme to detect the glucose concentration in whole blood. The nano-sized of MnO2 nanoparticles embedded in bovine serum albumin (BSA)-coated GO by in situ growth were evaluated focusing on the principle of HRP-mimic activity catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Furthermore, we constructed dual sensing platforms based on the combination of a plasma separation pad and GOD-GO/MnO2 for direct detection of glucose concentration in whole blood by colorimetric assay without blood sample pretreatment. As a proof-of-concept, a limit of detection of 3.1 mg dL-1 for glucose was obtained with a wide linear quantification range from 25 mg dL-1 to 300 mg dL-1 through visual observation and quantitative analysis, suggesting potential clinical applications in blood glucose monitoring for diabetic patients.

A high quantum yield (QY) is the key requirement for implementing carbon dots (CDs) in nearly all applications. In this work, blue emissive N-doped CDs with a QY of 83% and orange emissive N-doped CDs with a QY of 47% were successfully prepared using resorcinol and phloroglucin as carbon resources in formamide by one-step microwave synthesis, respectively. Formamide not only plays a role as the solvent but also takes part in the formation of the high QY CDs. It is demonstrated that the as-prepared blue- and orange-emitting N-doped CDs with a high QY can be uniformly dispersed into glue and be fabricated as CD/glue fluorescent composites for fluorescent films and fingerprint imaging. Furthermore, these CDs also show excellent cellular imaging capability.

The unique physical structure and chemical and electrical properties of graphene make it an ideal choice for sensor materials. The sensing platform of biomolecule functionalized graphene has received extensive attention due to its high sensitivity and selectivity, especially the biosensors constructed by combining antibodies, nucleic acids and enzymes that efficiently recognize specific targets with graphene having a large specific surface area and a fast electron transfer rate, which has become a significant research direction. In this paper, electrochemical biosensors based on graphene materials developed in recent years are summarized. The methods of functional modification of graphene, graphene oxide and reduced graphene oxide with antibodies, nucleic acids and enzymes are briefly described. In addition, the advantages and disadvantages of the constructed electrochemical biosensors in detecting pathogens and disease markers are also reviewed. Finally, we are optimistic about this prospect for the development direction and application prospects of such electrochemical biosensors.

Recently, water contamination caused by metal ions has become one of the most serious problems as it has caused several deaths and socioeconomic problems around the world. Hence, the fast and accurate detection of metal ions in aqueous media has become the most important area of research; from time to time, new probes have been designed for this purpose. Among the previously reported sensors, probes based on fluorescent organic nanoparticles (FONs) have been gaining tremendous attention due to their ease of preparation/fabrication, synthetic diversity according to targeted metal ions, quick response, high selectivity toward different analytes at lower concentrations, tenable optical properties, and less toxicity. This review comprises two main sections, wherein we have tried to summarize the key progresses made in this field. The first section summarizes the literature dealing with FON-based chemosensors, which are used for the detection of transition metal ions of silver, copper, chromium, cadmium, mercury, iron, and zinc. The second section focuses on FON-based chemosensors that…

Surface enhanced Raman spectroscopy (SERS) is a cutting edge analytical tool for trace analyte detection due to its highly sensitive, non-destructive and fingerprinting capability. Herein, we report the detection of multiple analytes from various mixtures using gold nanoparticles (NPs) and nanostructures (NSs) as SERS platforms. NPs and NSs were achieved through the simple approach of laser ablation in liquids (LAL) and their morphological studies were conducted with a UV-Visible absorption spectrometer, a high resolution transmission electron microscope (HRTEM) and a field emission scanning electron microscope (FESEM). The fabricated NPs/NSs allowed the sensitive and selective detection of different mixed compounds containing (i) rhodamine 6G (Rh6G) and methylene blue (MB), (ii) crystal violet (CV) and malachite green (MG), (iii) picric acid (explosive) and MB (dye), (iv) picric acid and 3-nitro-1,2,4- triazol-5-one (explosive, NTO) and (v) picric acid and 2,4-dinitrotoluene (explosive, DNT) using a portable Raman spectrometer. Thus, the obtained results demonstrate the capability…

An excessive cholesterol level can lead to cardiovascular diseases, such as stroke, hypertension, and myocardial infarction. A non-invasive, painless method of determining the cholesterol level in blood would improve the user's convenience. To provide rapid and accurate determination of cholesterol, we have developed a simple, disposable, enzyme-based electrochemical biosensor that can detect salivary cholesterol. It is possible to detect low concentrations of cholesterol in saliva using the optimized vertical structure of the platinum nano-cluster (Pt-NC) and the immobilization of a proper volume of an enzyme. The biosensor exhibited a linear range from 2 to 486 μM, the limit of detection was about 2 μM, and the sensitivity of the sensor was calculated to be 132 μA mM-1 cm-2. It also showed good specificity for ascorbic acid, uric acid, dopamine, glucose, and lactate. In a test with an actual sample, the performance of the biosensor was confirmed by measuring total cholesterol in the saliva of a patient with hyperlipidemia. The cholesterol levels measured in the saliva of three…

equilibration between the droplets and the protruding chains culminates in highly charged gaseous proteins, analogous to the collision-induced dissociation of multi-protein complexes. (iv) Denatured ESI supercharging also generates protein ions via the CEM. Supercharging agents stabilize protonated sites on the protein tail via charge-dipole interactions, causing the chain to acquire additional charge. There will likely be scenarios that fall outside of these four models, but it appears that the framework outlined here covers most of the experimentally relevant conditions.

particles per mL at a signal-to-noise ratio of 3. The aptasensor has been successfully used to detect exosomes in the serum.

in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications.

The development of viable point-of-care diagnostic formats is integral to achieving better patient care and improved outcomes. The need for robust and low-cost tests is especially important in under-resourced and rural settings. Perhaps the greatest challenge is ensuring that an untrained individual is capable of operating and interpreting the test, out with a care facility. Here we present a paper-based diagnostic device capable of sensing miR-29a using both colorimetric and surface enhanced Raman scattering (SERS) analysis. Rather, than carry out the two types of analyses in tandem, we envisage that the colorimetric output is easy enough to be interpreted by the untrained-individual administering the test to provide them with qualitative feedback. If deemed positive, the test can be further validated at a centralized care facility using a handheld-Raman spectrometer to provide a semi-quantitative result. Detection of miR-29a, a microRNA associated with myocardial infarction, was achieved at a level of pg μL-1 through the combination of three-dimensional paper-based microfluidics,…

MEPS, the acronym of microextraction by packed sorbent, is a simple, fast and user- and environmentally-friendly miniaturization of the popular solid-phase extraction technique (SPE). In fact, it has been widely shown that MEPS can easily replace SPE for most, if not all, previous applications. It can attain this with obvious gains in sample and solvent usage, which is greatly reduced without compromising the extraction efficiency. Furthermore, MEPS can be operated with semiautomatic electronic syringes, making it very reliable and versatile, particularly to handle very low and very high sample volumes. This review will focus on the strengths and weaknesses of this technique and the different MEPS architectures commercially available in the context of the MEPS applications reported in the last five years. Additionally, innovative improvements will be highlighted, particularly those related with new applications and recent MEPS configurations and sorbents, such as the controlled directional flow or the innovative μSPEed variant.

MicroRNAs (miRNAs) are attractive candidates for biomarkers for early cancer diagnosis, and play vital roles in physiological and pathological processes. In this work, we developed a colorimetric and fluorescent dual-mode sensor for miRNA detection based on the optical properties of gold nanoparticles (AuNPs) and the duplex-specific nuclease (DSN)-assisted signal amplification technique. In brief, FAM labelled hairpin probes (HPs) were immobilized on AuNPs, and fluorescence was efficiently quenched by the vicinity of the fluorophores to the AuNPs surface. In the presence of target miRNAs, the HPs could specifically hybridize with miRNAs and the DNA strand in the DNA/RNA heteroduplexes could be subsequently hydrolyzed by DSN. As a result, numbers of fluorophores were released into the solution, resulting in obvious fluorescence signal recovery. Meanwhile, the target miRNAs were able to participate in other hybridization reactions. With the DSN-assisted signal amplification technique, lots of gold nanoparticles were produced with short-chain DNA on their surface, which could aggregate…

Aflatoxin B1 (AFB1) pollution is one of the most serious problems for food safety. In this paper, a split-type photoelectrochemical (PEC) immunoassay was designed for sensitive detection of AFB1 in foodstuffs by using amorphous TiO2 with all-inorganic perovskite CsPbBr3 nanocrystals (CsPbBr3/a-TiO2). The a-TiO2 layer not only improved the stability of CsPbBr3 nanocrystals, but also facilitated charge transfer, which resulted in the increasing photocurrent of the nanocomposites. Initially, a competitive-type enzyme immunoreaction was executed on a high-binding microplate between the analyte and alkaline phosphatase (ALP)-labeled AFB1-bovine serum albumin (AFB1-BSA) conjugate. Accompanied by the formation of the immunocomplex, the carried ALP triggered enzymatic hydrolysis to generate ascorbic acid (AA, as an electron donor) for increasing the photocurrent of the CsPbBr3/a-TiO2-modified electrode. Coupling with the competitive enzyme immunoassay, the photocurrent of the modified electrode decreased with the increase of target AFB1 concentration in a dynamic working range from 0.01 ng…

A biomimetic fluorescent nanosensor based on molecularly imprinted polymers modified with carbon dots (CDs@MIPs) has been prepared for rapid, selective and sensitive detection of alpha-fetoprotein (AFP) in clinical samples. The nanosensor was produced using vinyl-functionalized CDs (V-CDs) as transducer elements and support materials, AFP as the template protein, N-isopropylacrylamide (NIPAM) and 4-vinylphenylbronic acid (VPBA) as the thermo-responsive and pH-responsive monomer, respectively, and ammonium peroxodisulphate (APS) and N,N'-methylene bisacrylamide (MBA) as the initiator and cross-linker, respectively. The newly synthesized nanosensor was characterized by FT-IR, TEM, XRD and elemental analysis, which unambiguously confirmed the successful formation of the nanosensor. The fluorescence quenching degree of CDs@MIPs exhibited a good linear response to AFP in a concentration range of 10 to 100 ng mL-1, the limit of detection (LOD) of 0.474 ng mL-1, and high recoveries at three spiking levels of AFP ranging from 97.05% to 102.00%, with relative standard deviations (RSDs) below…

An increasing number of studies have found that circulating exosomes play a vital role in the occurrence and metastasis of cancer. Therefore, a direct, sensitive and specific method for detection of tumor exosomes will contribute to the diagnosis and prognosis of cancer. In this work, we take advantage of the facile adaptability of aptamers to design an exosome quantitative method, which converts an exosome capture event to nucleic acid detection. With the help of a hairpin DNA cascade reaction (HDCR) and easy accessibility of DNA dendrimer self-assembly, dual signal amplification was achieved. A CD63 aptamer linked via a DNA probe to magnetic beads acts as the capture component. In the presence of target exosomes, aptamers identify and combine with exosomes, releasing the DNA probe as a trigger to initiate the HDCR (the first signal amplification process) by opening hairpin DNA (HP1) bound to gold nanoparticles (AuNPs). Fluorescently-labeled DNA dendrimers concatenate with HP1 as the second signal amplification stage to increase the signal-to-noise ratio. Under the optimal…

Boronic acids reversibly and covalently bind to Lewis bases and polyols, which facilitated the development of a large number of chemical sensors to recognize carbohydrates, catecholamines, ions, hydrogen peroxide, and so on. However, as the binding mechanism of boronic acids and analytes is not very clear, it is still a challenge to discover sensors with high affinity and selectivity. In this review, boronic acid sensors with two recognition sites, including diboronic acid sensors, and monoboronic acid sensors having another group or binding moiety, are summarized. Owing to double recognition sites working synergistically, the binding affinity and selectivity of sensors can be improved significantly. This review may help researchers to sort out the binding rules and develop ideal boronic acid-based sensors.

Exosomes are membrane-enclosed phospholipid extracellular vesicles with a variety of tumor antigens which can be applied in the diagnosis and treatment of cancer due to the high secretion on the surface of cancer cells. Until now, many research studies on exosomes have been reported, but convenient and low-cost detection methods still need to be developed. Recently, we have developed a sensitive, simple and low-cost colorimetric aptasensor by designing a hairpin-like structure, which combined the highly specific MUC1 aptamer with a hemin/G-quadruplex for the detection of breast cancer exosomes. The hemin/G-quadruplex toward H2O2 reduction was used to generate an evidently strong colorimetric response owing to acting as a HRP-mimicking DNAzyme. The aptasensor is regarded as an "on-off" type switch, which strictly controls the process of reaction responding to the existence or not of exosomes. In our study, associated exosome detection limits are 3.94 × 105 particles per mL, which showed a higher sensitivity compared to commercial ELISA. Our method not only exhibited the advantages of…

Herein, we report the antioxidant activity of cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) in pure and mixed solutions at different ratios, as well as of six different Cannabis sativa extracts containing various proportions of CBD and THC by using spectrophotometric (reducing power assay, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), hypochlorous acid (HOCl) scavenging assays) and electrochemical methods (cyclic voltammetry and differential pulse voltammetry). The isolated cannabinoids, the different stoichiometric ratios of CBD and THC, and the natural extracts proved to have remarkable antioxidant properties in all the methods employed in this work. The antioxidant activity of CBD and THC was compared against that of the well-defined antioxidants such as ascorbic acid (AA), resveratrol (Resv) and (-)-epigallocatechin-3-gallate (EGCG). Clear evidence of the synergistic and antagonistic effects between CBD and THC regarding to their antioxidant activities was observed. Moreover, a good correlation was obtained between…

Considerable evidence suggests breast cancer metastasis arises from cells undergoing epithelial-to-mesenchymal-transition (EMT) and cancer stem-like cells (CSCs). Using a microfluidic device that enriches migratory breast cancer cells with enhanced capacity for tumor formation and metastasis, we identified genes differentially expressed in migratory cells by high-throughput single-cell RNA-sequencing. Migratory cells exhibited overall signatures of EMT and CSCs with variable expression of marker genes, and they retained expression profiles of EMT over time. With single-cell resolution, we discovered intermediate EMT states and distinct epithelial and mesenchymal sub-populations of migratory cells, indicating breast cancer cells can migrate rapidly while retaining an epithelial state. Migratory cells showed differential profiles for regulators of oxidative stress, mitochondrial morphology, and the proteasome, revealing potential vulnerabilities and unexpected consequences of drugs. We also identified novel genes correlated with cell migration and outcomes in breast cancer as…