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Showing papers in "Analytical Chemistry in 2015"


Journal ArticleDOI
TL;DR: New advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014 are focused on to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors.
Abstract: Taking advantage of exceptional attributes, such as being easy-to-operate, economical, sensitive, portable, and simple-to-construct, in recent decades, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors.Various electrochemical devices, such as amperometric sensors, electrochemical impedance sensors, and electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications in the detection of chemical and biological targets in terms of electrochemical change of electrode interfaces. With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well-known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity, and biocompatibility to accelerate the signal transduction but also amplify biorecognition events with specifically designed signal tags, leading to highly sensitive biosensing. Significantly, extensive research on the construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing the wide application of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects and nanoengineered and/or nanostructured materials for the rational design of biofunctionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip and paper microfluidic devices.2 With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown a great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries. This Review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhanced electrochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are reviewed herein (Figure ​(Figure1).1). Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemical sensors and electrochemical methods to refer to other excellent literature for a broad scope in this area.3,4 However, due to the explosion of publications in this active field, we do not claim that this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out. Figure 1 Schematic illustration of electrochemical sensors and biosensors based on nanomaterials and nanostructures, in which electrochemical sensors for small molecular, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are demonstrated.

1,110 citations



Journal ArticleDOI
TL;DR: This review focuses on recent advances in Au NCs based sensing and imaging systems between 2012 and 2014 and examines their potential for the analysis of environmental and biological samples.
Abstract: F gold nanoclusters (Au NCs) or nanodots (NDs) with sizes smaller than 3 nm are a specific type of gold nanomaterials. In this review, Au NCs are used to represent fluorescent Au nanomaterials with sizes smaller than 3 nm. Unlike the most popular and well-known spherical, large gold nanoparticles, Au NCs do not exhibit surface plasmon resonance (SPR) absorption in the visible region but have fluorescence in the visible to near-infrared (NIR) region. With advantages of long lifetime, large Stokes shift, and biocompatibility, Au NCs have become interesting sensing and imaging materials. Although Au NCs prepared from Au in the presence of small thiol compounds such as 2-phenylethanethiol (PhCH2CH2SH) have been reported over the past decade, 5 their use for bioapplications have not been well recognized, mainly because of their low quantum yield (usually less than 1%), poor water dispersibility, photo and chemical instability, and difficulty for conjugation. In the past decade, many strategies for the preparation of stable, water dispersible, highly fluorescent, and biocompatible Au NCs have been reported. There are two major categories elucidating the recent advanced techniques for the preparation of Au NCs. The first category is through etching of larger sizes of nonfluorescent gold nanoparticles (Au NPs) by thiol compounds such as mercaptopropionic acid. The second category is from reduction of Au in the presence of a ligand or template (protein) such as bovine serum albumin (BSA). The optical properties of biocompatible Au NCs are dependent on their size, surface ligand or template, and the surrounding medium, and thus they can be studied to develop sensitive and selective sensing and imaging systems for the detection of various analytes. The growing popularity of Au NCs in analytical applications has been realized in these few years. Several excellent review papers dealing with Au NCs from the viewpoint of analytical chemistry have been reported to highlight their potential for the analysis of environmental and biological samples. This review focuses on recent advances in Au NCs based sensing and imaging systems between 2012 and 2014. Current challenges and future prospects of Au NCs for fundamental studies and analytical applications will be provided.

683 citations


Journal ArticleDOI
TL;DR: UniDec (Universal Deconvolution), software that provides a rapid, robust, and flexible deconvolution of mass spectra and ion mobility-mass spectra with minimal user intervention is developed, using systems of increasing complexity.
Abstract: Interpretation of mass spectra is challenging because they report a ratio of two physical quantities, mass and charge, which may each have multiple components that overlap in m/z. Previous approaches to disentangling the two have focused on peak assignment or fitting. However, the former struggle with complex spectra, and the latter are generally computationally intensive and may require substantial manual intervention. We propose a new data analysis approach that employs a Bayesian framework to separate the mass and charge dimensions. On the basis of this approach, we developed UniDec (Universal Deconvolution), software that provides a rapid, robust, and flexible deconvolution of mass spectra and ion mobility-mass spectra with minimal user intervention. Incorporation of the charge-state distribution in the Bayesian prior probabilities provides separation of the m/z spectrum into its physical mass and charge components. We have evaluated our approach using systems of increasing complexity, enabling us to ...

602 citations


Journal ArticleDOI
TL;DR: This preliminary investigation indicates that the tattoo-based iontophoresis-sensor platform holds considerable promise for efficient diabetes management and can be extended toward noninvasive monitoring of other physiologically relevant analytes present in the interstitial fluid.
Abstract: We present a proof-of-concept demonstration of an all-printed temporary tattoo-based glucose sensor for noninvasive glycemic monitoring. The sensor represents the first example of an easy-to-wear flexible tattoo-based epidermal diagnostic device combining reverse iontophoretic extraction of interstitial glucose and an enzyme-based amperometric biosensor. In-vitro studies reveal the tattoo sensor’s linear response toward physiologically relevant glucose levels with negligible interferences from common coexisting electroactive species. The iontophoretic-biosensing tattoo platform is reduced to practice by applying the device on human subjects and monitoring variations in glycemic levels due to food consumption. Correlation of the sensor response with that of a commercial glucose meter underscores the promise of the tattoo sensor to detect glucose levels in a noninvasive fashion. Control on-body experiments demonstrate the importance of the reverse iontophoresis operation and validate the sensor specificity....

541 citations


Journal ArticleDOI
TL;DR: It is demonstrated that such novel Au NPs-N-GQDs nanocomposite is promising for fabrication of nonenzymatic H2O2 biosensors and has shown great potential applications for detection of H 2O2 levels in human serum samples and that released from human cervical cancer cells with satisfactory results.
Abstract: In this work, we report a green and simple strategy for the in situ growth of surfactant-free Au nanoparticles (Au NPs) on nitrogen-doped graphene quantum dots (Au NPs–N-GQDs). The formation of hybrid was achieved by just mixing the N-GQDs and HAuCl4·4H2O without addition of any other reductant and surfactant. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) characterizations clearly showed the formation of Au nanoparticles with predominantly exposed (111) facets which can provide more adsorption sites. Such nonsurfactant-capped Au NPs can provide naked catalytic surface with highly electrocatalytic activity. The Au NPs–N-GQDs exhibit high sensitivity and selectivity for electrochemical detection of hydrogen peroxide (H2O2) with a low detection limit of 0.12 μM and sensitivity of 186.22 μA/mM cm2. Importantly, the Au NPs–N-GQDs-based electrochemical biosensor has shown great potential applications for detection of H2O2 levels in ...

498 citations


Journal ArticleDOI
TL;DR: A robust protocol which was nonselective and reproducible, and a considerable reduction in analysis time compared with previous methods, is likely to provide an essential tool for further research into the pathways by which microplastics enter the environment.
Abstract: Microplastics (<5 mm) have been documented in environmental samples on a global scale. While these pollutants may enter aquatic environments via wastewater treatment facilities, the abundance of microplastics in these matrices has not been investigated. Although efficient methods for the analysis of microplastics in sediment samples and marine organisms have been published, no methods have been developed for detecting these pollutants within organic-rich wastewater samples. In addition, there is no standardized method for analyzing microplastics isolated from environmental samples. In many cases, part of the identification protocol relies on visual selection before analysis, which is open to bias. In order to address this, a new method for the analysis of microplastics in wastewater was developed. A pretreatment step using 30% hydrogen peroxide (H2O2) was employed to remove biogenic material, and focal plane array (FPA)-based reflectance micro-Fourier-transform (FT-IR) imaging was shown to successfully im...

426 citations


Journal ArticleDOI
TL;DR: The wave mercury-removing device is very important for Pb isotope ratio and accessory mineral U-Pb dating analysis, where removal of the mercury from the background gas and sample aerosol particles is highly desired.
Abstract: A novel "wave" signal-smoothing and mercury-removing device has been developed for laser ablation quadrupole and multiple collector ICPMS analysis. With the wave stabilizer that has been developed, the signal stability was improved by a factor of 6.6-10 and no oscillation of the signal intensity was observed at a repetition rate of 1 Hz. Another advantage of the wave stabilizer is that the signal decay time is similar to that without the signal-smoothing device (increased by only 1-2 s for a signal decay of approximately 4 orders of magnitude). Most of the normalized elemental signals (relative to those without the stabilizer) lie within the range of 0.95-1.0 with the wave stabilizer. Thus, the wave stabilizer device does not significantly affect the aerosol transport efficiency. These findings indicate that this device is well-suited for routine optimization of ICPMS, as well as low repetition rate laser ablation analysis, which provides smaller elemental fractionation and better spatial resolution. With the wave signal-smoothing and mercury-removing device, the mercury gas background is reduced by 1 order of magnitude. More importantly, the (202)Hg signal intensity produced in the sulfide standard MASS-1 by laser ablation is reduced from 256 to 0.7 mV by the use of the wave signal-smoothing and mercury-removing device. This result suggests that the mercury is almost completely removed from the sample aerosol particles produced by laser ablation with the operation of the wave mercury-removing device. The wave mercury-removing device that we have designed is very important for Pb isotope ratio and accessory mineral U-Pb dating analysis, where removal of the mercury from the background gas and sample aerosol particles is highly desired. The wave signal-smoothing and mercury-removing device was applied successfully to the determination of the (206)Pb/(204)Pb isotope ratio in samples with low Pb content and/or high Hg content.

330 citations


Journal ArticleDOI
TL;DR: The intent of this review is to focus primarily on recent developments made with regard to temporally dispersive ion mobility techniques (drift tubes and traveling wave separators), with an emphasis on their use specifically in IM-MS instrumentation and methods.
Abstract: The field of ion mobility-mass spectrometry (IM-MS) has grown with significant momentum in recent years in both fundamental advances and pioneering applications. A search of the terms “ion mobility” and “mass spectrometry” returns more than 2 000 papers, with over half of these being published in the past 4 years (Figure ​(Figure1,1, left). This increased interest has been motivated in large part by improved technologies which have enabled contemporary IM-MS to be amendable to a variety of samples in biology and medicine with high sensitivity, resolving power, and sample throughput. Figure 1 (Left) Histogram of the number of publications published per year in ion mobility and ion mobility-mass spectrometry. Note that the scale is truncated at 300 to highlight the number of publications specifically utilizing IM-MS. Further distinction is ... Highlights of the historical development of the field are presented in Figure ​Figure1,1, right. Ion mobility and mass spectrometry trace their foundations to the X-ray experiments of Thomson and Rutherford in the late 1800s,1 with Tyndall making significant improvements in the analytical capabilities of ion mobility around the 1930s.2,3 During this early era of discovery, a variety of ion mobility experimental parameters were explored, including differences in pressure,4,5 temperature,6,7 electric field,8 and the ion residence time (age) in the drift region.9 Hybrid IM-MS instruments of various configurations were developed by several groups in the 1960s to study gas-phase ion chemistry.10−12 Ion mobility measurements were used by Dole in the earliest development of electrospray ionization (ESI).13,14 Following commercialization,15 ion mobility instrumentation was used for structure-based characterization16 and differentiation of chemical isomers.17,18 In 1982, laser ionization was demonstrated with ion mobility as a means of generating simplified mobility spectra based on protonated species.19 The features which define modern IM-MS, namely, high resolution, high sensitivity, and broad sample compatibility, were developed in the 1990s and coincided with the rapid development of MS in response to the introduction of ESI and MALDI sample ionization.20−22 The last 2 decades saw significant improvements made in the coupling of IM to MS, notably the use of electrodynamic fields to confine, transfer, and focus ions across disparate pressure regions into high vacuum. An interesting observation to be made in this historical analysis is that many of the features we associate with contemporary ion mobility technology were key aspects of early ion mobility instrument design. Several noteworthy reviews of IM-MS have been published, which cover many aspects of the IM-MS technique and range of applications.23−28 A number of influential books covering various aspects of the ion mobility field are also available.29−34 Of particular relevance is Mason and McDaniel’s Transport Properties of Ions in Gases,35 which was recently republished by the American Society for Mass Spectrometry in their classic books series. Though last revised in 1988, this book is still widely considered the seminal treatment of the motion of ions in gases. The technologies and application areas which IM-MS now encompasses has expanded to such a breadth that new reviews covering IM-MS and related areas now appear every few years in the literature. A comprehensive and critical review of the field as a whole is no longer appropriate nor tractable, and as such it is the intent of this review to focus primarily on recent developments made with regard to temporally dispersive ion mobility techniques (drift tubes and traveling wave separators), with an emphasis on their use specifically in IM-MS instrumentation and methods. This focus is selected because of the recent commercial offerings in this regard that have become widely used in many research environments. The present review is not intended to be comprehensive of the ion mobility advances but rather focuses on time-dispersive IM-MS instrumentation over the past few years.

302 citations



Journal ArticleDOI
TL;DR: An effective and facile fluorescence sensing approach for the determination of 2,4,6-trinitrophenol using the chemically oxidized and liquid exfoliated graphitic carbon nitride (g-C3N4) nanosheets was developed and has potential application for visual detection of TNP in natural water samples for public safety and security.
Abstract: An effective and facile fluorescence sensing approach for the determination of 2,4,6-trinitrophenol (TNP) using the chemically oxidized and liquid exfoliated graphitic carbon nitride (g-C3N4) nanosheets was developed. The strong inner filter effect and molecular interactions (electrostatic, π–π, and hydrogen bonding interactions) between TNP and the g-C3N4 nanosheets led to the fluorescence quenching of the g-C3N4 nanosheets with efficient selectivity and sensitivity. Under optimal conditions, the limit of detection for TNP was found to be 8.2 nM. The proposed approach has potential application for visual detection of TNP in natural water samples for public safety and security.

Journal ArticleDOI
TL;DR: The as-proposed label-free and enzyme-free homogeneous electrochemical strategy may become an alternative method for simple, sensitive, and selective miRNA detection, and it has great potential to be applied in miRNA-related clinical diagnostics and biochemical research.
Abstract: Homogenous electrochemical biosensing strategies have attracted substantial attention, because of their advantages of being immobilization-free and having rapid response and improved recognition efficiency, compared to heterogeneous biosensors; however, the high cost of labeling and the strict reaction conditions of tool enzymes associated with current homogeneous electrochemical methods limit their potential applications. To address these issues, herein we reported, for the first time, a simple label-free and enzyme-free homogeneous electrochemical strategy based on hybridization chain reaction (HCR) for sensitive and highly specific detection of microRNA (miRNA). The target miRNA triggers the HCR of two species of metastable DNA hairpin probes, resulting in the formation of multiple G-quadruplex-incorporated long duplex DNA chains. Thus, with the electrochemical indicator Methylene Blue (MB) selectively intercalated into the duplex DNA chain and the multiple G-quadruplexes, a significant electrochemical signal drop is observed, which is dependent on the concentration of the target miRNA. Thus, using this "signal-off" mode, a simple, label-free and enzyme-free homogeneous electrochemical strategy for sensitive miRNA assay is readily realized. This strategy also exhibits excellent selectivity to distinguish even single-base mismatched miRNA. Furthermore, this method also exhibits additional advantages of simplicity and low cost, since both expensive labeling and sophisticated probe immobilization processes are avoided. Therefore, the as-proposed label-free and enzyme-free homogeneous electrochemical strategy may become an alternative method for simple, sensitive, and selective miRNA detection, and it has great potential to be applied in miRNA-related clinical diagnostics and biochemical research.

Journal ArticleDOI
Lei Li1, Shuijian He1, Minmin Liu1, Chunmei Zhang1, Wei Chen1 
TL;DR: The present work demonstrates that the 3D mesoporous SnO2/rGO composites with extremely large surface area and stable nanostructure are excellent candidate materials for gas sensing.
Abstract: A facile and cost-efficient hydrothermal and lyophilization two-step strategy has been developed to prepare three-dimensional (3D) SnO2/rGO composites as NO2 gas sensor. In the present study, two different metal salt precursors (Sn2+ and Sn4+) were used to prepare the 3D porous composites. It was found that the products prepared from different tin salts exhibited different sensing performance for NO2 detection. The scanning electron microscopy and transmission electron microscopy characterizations clearly show the macroporous 3D hybrids, nanoporous structure of reduce graphene oxide (rGO), and the supported SnO2 nanocrystals with an average size of 2–7 nm. The specific surface area and porosity properties of the 3D mesoporous composites were analyzed by Braunauer–Emmett–Teller method. The results showed that the SnO2/rGO composite synthesized from Sn4+ precursor (SnO2/rGO-4) has large surface area (441.9 m2/g), which is beneficial for its application as a gas sensing material. The gas sensing platform fab...

Journal ArticleDOI
TL;DR: Full integration of sample preparation with LAMP amplification and end point detection with a limit of detection of 5 cells is demonstrated and it is shown that the method used to prepare sample enables concentration of DNA from sample volumes commonly available from fingerstick blood draw.
Abstract: Clinical tests based on primer-initiated amplification of specific nucleic acid sequences achieve high levels of sensitivity and specificity. Despite these desirable characteristics, these tests have not reached their full potential because their complexity and expense limit their usefulness to centralized laboratories. This paper describes a device that integrates sample preparation and loop-mediated isothermal amplification (LAMP) with end point detection using a hand-held UV source and camera phone. The prototype device integrates paper microfluidics (to enable fluid handling) and a multilayer structure, or a “paper machine”, that allows a central patterned paper strip to slide in and out of fluidic path and thus allows introduction of sample, wash buffers, amplification master mix, and detection reagents with minimal pipetting, in a hand-held, disposable device intended for point-of-care use in resource-limited environments. This device creates a dynamic seal that prevents evaporation during incubatio...

Journal ArticleDOI
Yi Zhang1, Guang Ming Zeng1, Lin Tang1, Chen Jun1, Yuan Zhu1, Xiao Xiao He1, Yan He1 
TL;DR: An electrochemical sensor was developed for attomolar Hg(2+) detection and was demonstrated to achieve excellent detectability, which may be applied to development of ultrasensitive detection strategies.
Abstract: An electrochemical sensor was developed for attomolar Hg2+ detection. Three single-stranded DNA probes were rationally designed for selective and sensitive detection of the target, which combined T...

Journal ArticleDOI
TL;DR: The results indicate that adding CCS to databases and lipidomics workflows increases the specificity and selectivity of analysis, thus improving the confidence in lipid identification compared to traditional analytical approaches.
Abstract: Despite recent advances in analytical and computational chemistry, lipid identification remains a significant challenge in lipidomics. Ion-mobility spectrometry provides an accurate measure of the molecules' rotationally averaged collision cross-section (CCS) in the gas phase and is thus related to ionic shape. Here, we investigate the use of CCS as a highly specific molecular descriptor for identifying lipids in biological samples. Using traveling wave ion mobility mass spectrometry (MS), we measured the CCS values of over 200 lipids within multiple chemical classes. CCS values derived from ion mobility were not affected by instrument settings or chromatographic conditions, and they were highly reproducible on instruments located in independent laboratories (interlaboratory RSD < 3% for 98% of molecules). CCS values were used as additional molecular descriptors to identify brain lipids using a variety of traditional lipidomic approaches. The addition of CCS improved the reproducibility of analysis in a liquid chromatography-MS workflow and maximized the separation of isobaric species and the signal-to-noise ratio in direct-MS analyses (e.g., "shotgun" lipidomics and MS imaging). These results indicate that adding CCS to databases and lipidomics workflows increases the specificity and selectivity of analysis, thus improving the confidence in lipid identification compared to traditional analytical approaches. The CCS/accurate-mass database described here is made publicly available.

Journal ArticleDOI
TL;DR: A simple and highly efficient method for dopamine (DA) detection using water-soluble silicon nanoparticles (SiNPs) was reported, with a detection limit of 0.3 nM, which is the lowest limit reported so far.
Abstract: A simple and highly efficient method for dopamine (DA) detection using water-soluble silicon nanoparticles (SiNPs) was reported. The SiNPs with a high quantum yield of 23.6% were synthesized by using a one-pot microwave-assisted method. The fluorescence quenching capability of a variety of molecules on the synthesized SiNPs has been tested; only DA molecules were found to be able to quench the fluorescence of these SiNPs effectively. Therefore, such a quenching effect can be used to selectively detect DA. All other molecules tested have little interference with the dopamine detection, including ascorbic acid, which commonly exists in cells and can possibly affect the dopamine detection. The ratio of the fluorescence intensity difference between the quenched and unquenched cases versus the fluorescence intensity without quenching (ΔI/I) was observed to be linearly proportional to the DA analyte concentration in the range from 0.005 to 10.0 μM, with a detection limit of 0.3 nM (S/N = 3). To the best of our ...


Journal ArticleDOI
TL;DR: This Review focuses on recent advances in nan ofabrication techniques as well as studies of fundamental transport in nanofluidic devices, and limited the scope of this Review to studies with nanopores, nanochannels, and nanopipets.
Abstract: Ion, particle, and fluid transport in nanofluidic devices has received considerable attention over the past two decades due to unique transport properties exhibited at the nanoscale.1,2 Phenomena such as double layer overlap, high surface-to-volume ratios, surface charge, ion-current rectification, and entropic barriers can influence transport in and around nanofluidic structures because the length scales of these forces and the critical dimensions of the device are similar. Advances in micro- and nanofabrication techniques provide the ability to design a variety of well-defined nanofluidic geometries to study these phenomena and their effects on ion and fluid transport. Integration of micro- and nanofluidic structures into lab-on-a-chip devices permits increased functionality that is useful for a range of analytical applications.3,4 This Review focuses on recent advances in nanofabrication techniques as well as studies of fundamental transport in nanofluidic devices. Nanopores, nanochannels, and nanopipets are three common nanofluidic structures that have been influential in studying nanofluidic transport. Because of space limitations, we have limited the scope of this Review to studies with these three structures, and we focus our attention primarily on work published between January 2011 and August 2014. We do not discuss work with carbon nanotubes,5 nanomeshes,6 or nanowires.7 Figure ​Figure11 shows examples of the three nanofluidic geometries discussed here. Nanopores are typically formed perpendicular to the plane of a substrate and are characterized by a critical limiting dimension, which is measured by scanning electron microscopy (SEM), transmission electron microscopy (TEM), or conductance measurements. Pores are fabricated in a variety of materials, e.g., poly(carbonate), poly(ethylene terephthalate), or silicon nitride, and can have an asymmetric (Figure ​(Figure1a)1a) or symmetric (Figure ​(Figure1b)1b) shape, depending on the fabrication technique. Symmetric pores are either cylindrically shaped with a constant critical dimension determined by electron microscopy or hourglass-shaped with a critical dimension at the center of the pore. Although electron microscopy is capable of measuring exterior pore dimensions, the exact inner geometry is often unknown and may contain an asymmetry between two symmetric features, e.g., cigar-shaped pores. Asymmetric nanopores typically have a narrow tip and a wide base with a funnel-shaped geometry along the pore axis. Tip and base dimensions are measured by SEM, but the exact pore geometry is often unknown. Nanochannels often refer to in-plane structures with either symmetric (Figure ​(Figure1c)1c) or asymmetric (Figure ​(Figure1d)1d) geometries. Channels may be confined to the nanoscale in depth, width, or both, depending on the fabrication method. Nanochannels are commonly fabricated in glass and polymer substrates and characterized by SEM and atomic force microscopy (AFM). The in-plane nature of these channels allows the integration of well-defined features into more complex geometries, and any two-dimensional (2D) channel architecture can be designed. Nanopipets are specialized nanopores fabricated from pulled glass or fused-silica capillaries (Figure ​(Figure1e,f). The1e,f). The geometry of a nanopipet is conically shaped with a critical tip diameter of tens to hundreds of nanometers, which can be measured by electron microscopy. Unlike nanopores and nanochannels, nanopipets can be easily coupled with position control, which allows the tip of the nanopipets to be positioned in specific locations or used in scanned probe microscopies. Figure 1 Nanopores, nanochannels, and nanopipets are three common nanofluidic platforms. Nanopores are typically out-of-plane structures and have either an asymmetric or symmetric geometry. Conical nanopores have a wide base as shown in panel a that tapers to ...

Journal ArticleDOI
TL;DR: A ratiometric fluorescent assay based on the ALP-induced destruction of the supramolecular ICP network and the release of coumarin is developed and is employed for ALP inhibitor evaluation.
Abstract: This study demonstrates a novel ratiometric fluorescent method for real-time alkaline phosphatase (ALP) activity assay with stimulus responsive infinite coordination polymer (ICP) nanoparticles as the probe. The ICP nanoparticles used in this study are composed of two components; one is the supramolecular ICP network formed with guanine monophosphate (GMP) as the ligand and Tb3+ as the central metal ion, and the other is a fluorescent dye, i.e., 7-amino-4-methyl coumarin (coumarin) encapsulated into the ICP network. Upon being excited at 315 nm, the ICP network itself emits green fluorescence at 552 nm. Coumarin dye encapsulated in the ICP network emits weak fluorescence at 450 nm upon excitation at the same wavelength (315 nm), and this fluorescence emission becomes strong when the encapsulated dye is released from the network into the solution phase. Hence, we develop a ratiometric fluorescent assay based on the ALP-induced destruction of the supramolecular ICP network and the release of coumarin. This ...

Journal ArticleDOI
TL;DR: RawConverter, a stand-alone software tool, to improve data extraction on RAW files from high-resolution Thermo Fisher mass spectrometers, which generates output into MS1/MS2/MS3, MGF, or mzXML file formats, which satisfies the format requirements for most data identification and quantification tools.
Abstract: Extraction of data from the proprietary RAW files generated by Thermo Fisher mass spectrometers is the primary step for subsequent data analysis. High resolution and high mass accuracy data obtained by state-of-the-art mass spectrometers (e.g., Orbitraps) can significantly improve both peptide/protein identification and quantification. We developed RawConverter, a stand-alone software tool, to improve data extraction on RAW files from high-resolution Thermo Fisher mass spectrometers. RawConverter extracts full scan and MSn data from RAW files like its predecessor RawXtract; most importantly, it associates the accurate precursor mass-to-charge (m/z) value with the tandem mass spectrum. RawConverter accepts RAW data generated by either data-dependent acquisition (DDA) or data-independent acquisition (DIA). It generates output into MS1/MS2/MS3, MGF, or mzXML file formats, which fulfills the format requirements for most data identification and quantification tools. Using the tandem mass spectra extracted by R...

Journal ArticleDOI
Xiaohua Zhu1, Tingbi Zhao1, Zhou Nie2, Yang Liu1, Shouzhuo Yao2 
TL;DR: The proposed sensing systems represented excellent sensitivity and selectivity for AA analysis in human biological fluids, providing a valuable platform for AA sensing in clinic diagnostic and drug screening.
Abstract: Highly photoluminescent nitrogen-doped carbon nanoparticles (N-CNPs) were prepared by a simple and green route employing sodium alginate as a carbon source and tryptophan as both a nitrogen source and a functional monomer. The as-synthesized N-CNPs exhibited excellent water solubility and biocompatibility with a fluorescence quantum yield of 47.9%. The fluorescence of the N-CNPs was intensively suppressed by the addition of ascorbic acid (AA). The mechanism of the fluorescence suppression of the N-CNPs was investigated, and the synergistic action of the inner filter effect (IFE) and the static quenching effect (SQE) contributed to the intensive fluorescence suppression, which was different from those reported for the traditional redox-based fluorescent probes. Owing to the spatial effect and hydrogen bond between the AA and the groups on the N-CNP surface, excellent sensitivity and selectivity for AA detecting was obtained in a wide linear relationship from 0.2 μM to 150 μM. The detection limit was as low...

Journal ArticleDOI
TL;DR: A novel nanosensor was developed to discriminate cysteine from homocysteine (Hcy) and glutathione (GSH) with multiple signals: colorimetric, photoluminescence (PL), and up-conversional photolumscence (UCP) and was successfully applied for the detection of Cys in human serum with the detection limit of 4 nM.
Abstract: Biological thiols play a critical role in biological processes and are involved in a variety of diseases. The discrimination detection of biological thiols is of increasing importance in clinical diagnosis. In this paper, a novel nanosensor was developed to discriminate cysteine (Cys) from homocysteine (Hcy) and glutathione (GSH) with multiple signals: colorimetric, photoluminescence (PL), and up-conversional photoluminescence (UCP). The nanosensor (NC-dots/AuNPs) was constructed by nitrogen-doped carbon dots (NC-dots) and gold nanoparticles (AuNPs) through assembling NC-dots “shell” on AuNPs and showed the obvious different response to Cys, Hcy, and GSH with colorimetric, PL, and UCP signals. The discrimination effect for Cys is originated from conformations and interaction difference of the thiols groups in Cys and Hcy and/or GSH with AuNPs. Among them, only Cys can quickly penetrate into the NC-dots “shell” of the composite and induce the dispersing of the aggregated NC-dots/AuNPs, which lead to the co...

Journal ArticleDOI
TL;DR: A novel aptasensor for ochratoxin A (OTA) detection based on a screen-printed carbon electrode modified with polythionine (PTH) and iridium oxide nanoparticles (IrO2 NPs) is presented, obtaining one of the lowest limits of detection reported so far for label-free impedimetric detection of OTA.
Abstract: In this article, a novel aptasensor for ochratoxin A (OTA) detection based on a screen-printed carbon electrode (SPCE) modified with polythionine (PTH) and iridium oxide nanoparticles (IrO2 NPs) is presented. The electrotransducer surface is modified with an electropolymerized film of PTH followed by the assembly of IrO2 NPs on which the aminated aptamer selective to OTA is exchanged with the citrate ions surrounding IrO2 NPs via electrostatic interactions with the same surface. Electrochemical impedance spectroscopy (EIS) in the presence of the [Fe(CN)6]−3/–4 redox probe is employed to characterize each step in the aptasensor assay and also for label-free detection of OTA in a range between 0.01 and 100 nM, obtaining one of the lowest limits of detection reported so far for label-free impedimetric detection of OTA (14 pM; 5.65 ng/kg). The reported system also exhibits a high reproducibility, a good performance with a white wine sample, and an excellent specificity against another toxin present in such sa...

Journal ArticleDOI
TL;DR: Measurements of tryptophan fluorescence (WF) for total protein determination in whole tissue lysates and for peptide quantification in protein digests demonstrate that the fluorescence spectrometry of tryPTophan offers a simple, sensitive, and direct method for protein and peptide assays.
Abstract: The determination of total protein content is one of the most frequent analytical tasks in biochemistry and molecular biology. Here we evaluate measurements of tryptophan fluorescence (WF) for total protein determination in whole tissue lysates and for peptide quantification in protein digests. We demonstrate that the fluorescence spectrometry of tryptophan offers a simple, sensitive, and direct method for protein and peptide assays. The WF assay is fully compatible with SDS and other solutes that are commonly used for lysis of tissue and cells. We found that the content of tryptophan varies only a little between mouse tissues (1.16 ± 0.08% of total amino acids) and is similar in human cells (1.19 ± 0.06%). Therefore, free tryptophan can be used as a universal standard. We show that the assay can be carried out on a standard fluorescence spectrometer with cuvettes as well as in a 96-well format using a plate reader. The method is particularly suitable for determination of peptide content in diluted samples. Notably, the whole sample can be recovered after the measurement.

Journal ArticleDOI
Yinhui Li1, Yijun Wang1, Sheng Yang1, Yirong Zhao1, Lin Yuan1, Jing Zheng1, Ronghua Yang1 
TL;DR: NIR-Ratio-BTZ is a highly sensitive ratiometric pH probe in vivo, giving it potential for biological applications and an ideal pK(a) value for monitoring the minor fluctuations of physiological pH near neutrality.
Abstract: Intracellular pH is an important parameter associated with cellular behaviors and pathological conditions. Quantitative sensing pH and monitoring its changes by near-infrared (NIR) fluorescence imaging with high resolution in living systems are essential but challenging due to the lack of effective probes. To achieve good adaptability, in this study, a class of resolution-tunable ratiometric NIR fluorescent probes, which possess a stable NIR hemicyanine skeleton bearing different substituents, are rationally designed and synthesized, enabling detection through noninvasive optical imaging of organisms. Based on the protonation/deprotonation of the hydroxy group, a marked NIR emission shift provides a ratio signal in response to pH. Meanwhile, two states exhibit good photostability, sensitivity and reversibility, conducive to longtime monitoring of persistent pH changes without disturbance of other biological active species. Among the series, NIR-Ratio-BTZ modified with an electron-withdrawing substituent o...

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TL;DR: A simple, sensitive inner filter effect (IFE)-based fluorescent assay for sensing H2O2 and cholesterol, developed using poly(vinylpyrrolidone)-protected gold nanoparticles and fluorescent BSA-protected gold nanoclusters as an IFE absorber/fluorophore pair.
Abstract: We developed a simple, sensitive inner filter effect (IFE)-based fluorescent assay for sensing H2O2 and cholesterol. In the process, poly(vinylpyrrolidone)-protected gold nanoparticles (PVP-AuNPs) and fluorescent BSA-protected gold nanoclusters (BSA-AuNCs) were used as an IFE absorber/fluorophore pair. PVP-AuNPs can be a powerful absorber to influence the emission of the fluorophore, BSA-AuNCs, in the IFE-based fluorescent assays. That is due to the high extinction coefficient of AuNPs and the complementary overlap between the surface plasmon resonance (SPR) absorption of PVP-AuNPs and the excitation of BSA-AuNCs. The PVP-Au seeds, produced by directly mixing PVP with HAuCl4, were able to catalyze H2O2 to enlarge AuNPs. The SPR absorption of PVP-AuNPs was enhanced with an increased concentration of H2O2 and, subsequently, induced significant fluorescence quenching of BSA-AuNCs. The IFE-based fluorescent assay enabled the detection of H2O2 and generation of H2O2 in the presence of O2/cholesterol and choles...


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TL;DR: Electrochemiluminescent and photoelectrochemical properties and mechanisms of semiconductor quantum dots (QDs) are reviewed, with emphasis on their specific fundamentals and concise comparison on their similarities and differences.
Abstract: In this Feature, electrochemiluminescent (ECL) and photoelectrochemical (PEC) properties and mechanisms of semiconductor quantum dots (QDs) are reviewed, with emphasis on their specific fundamentals and concise comparison on their similarities and differences. With recent illustrative examples of bioanalytical applications, the main signaling strategies for QDs-based ECL and PEC bioanalysis are then highlighted. The future prospects in this field are also discussed.

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TL;DR: In this work, single-stranded DNA aptamers against cTnI were identified by the Systematic Evolution of Ligands by Exponential enrichment (SELEX) method and exhibited a high selectivity and sensitivity toward both cTNI and the cardiac Troponin complex.
Abstract: Cardiac troponin I (cTnI) is well-known as a promising biomarker for the early diagnosis of acute myocardial infarction (AMI). In this work, single-stranded DNA aptamers against cTnI were identified by the Systematic Evolution of Ligands by Exponential enrichment (SELEX) method. The aptamer candidates exhibited a high selectivity and sensitivity toward both cTnI and the cardiac Troponin complex. The binding affinities of each aptamer were evaluated based on their dissociation constants (Kd) by surface plasma resonance. The Tro4 aptamer that had the highest binding capacity to cTnI showed a very low Kd value (270 pM) compared with that of a cTnI antibody (20.8 nM). Furthermore, we designed a new electrochemical aptasensor based on square wave voltammetry using ferrocene-modified silica nanoparticles. The developed aptasensor demonstrated an excellent analytical performance for cTnI with a wide linear range of 1–10 000 pM in a buffer and a detection limit of 1.0 pM (24 pg/mL; S/N = 3), which was noticeably ...