Search

Per- and polyfluoroalkyl substances (PFAS) are emerging as harmful environmental micropollutants. Generally, PFAS species are quantified by mass spectrometry, for which a collected sample is taken to a centralized facility. Robust techniques to quantify PFAS in the field are necessary to diagnose environmental contamination at the earliest onset of pollution. Here, we developed a molecularly imprinted polymer (MIP) electrode for the detection of perfluorooctanesulfonate (PFOS) and explored the MIP surface and the effects of interfering molecules. MIPs were formed by the anodic deposition of o -phenylenediamine ( o -PD) in the presence of PFOS template molecules on a glassy carbon macroelectrode. The performance of the resulting MIP electrode was evaluated by the current obtained from the oxidation of ferrocene carboxylic acid as the electrochemical probe. The MIP electrode was able to detect PFOS with a detection limit of 0.05 nM, which is lower than the health advisory limit of 0.14 nM reported by the U.S. EPA. To better understand PFOS association into the MIP, a Langmuir binding model was developed based on the changes in electrochemical responses of the MIP. Fitting the model to the experimental data gave an association constant ( K A ) of 4.95 × 10 12 over a PFOS concentration range of 0 to 0.05 nM. The binding isotherm of other commonly found substances in contaminated water sources such as chloride, humic acid, perfluorooctanoic acid (PFOA), and perfluorobutanesulfonate (PFBS) was also investigated. In the case of chloride and humic acid, the calculated K A values of 9.05 × 10 7 and 6.01 × 10 5 , respectively, indicate relatively weak adsorption of these species on the MIP. However, PFOA, which is the carboxylate analog of PFOS, revealed a very close K A value (3.41 × 10 12 ) to PFOS. A greater K A value (1.43 × 10 13 ) was obtained for PFBS, which possesses the same functional group and a smaller molecular size compared to PFOS. The presented platform emphasizes the necessity to develop new strategies to make MIP sensors more specific if practical applications are to be pursued.

Synthesis of red emissive carbon dots (CDs) is highly desirable for sensing applications, as they still remain as bottlenecks in terms of precursor synthesis and product purification. Herein, we have designed a new strategy for realizing efficient red emissive CD optimal emission at 610 nm (fluorescence quantum yield ca. 24.0%) based on solvothermal treatment of citric acid and thiourea using dimethylformamide as solvent. Further investigations reveal that the conjugating sp 2 -domain controlling the incorporation of nitrogen and surface engineering are mainly responsible for the obtained red emission of CDs. Taking advantage of optical properties and abundant surface functional groups, CDs were considered to facilely construct a ratiometric fluorescent platform for quantifying trace levels of organophosphorus pesticides (OPs). Combining the acetylcholinesterase-mediated polymerization of dopamine and the inhibition of pesticide toward the enzyme, the degree of polymerization of dopamine rationally depends on the concentration of OPs. By measuring the fluorescence intensity ratio, the proposed platform exhibited highly selective and robust performance toward OPs, displaying ultrasensitive recognition in the pg L -1 level. The multiexcitation format could efficiently shield background interference from complex samples by introducing a self-calibrated reference signal, which affords accurate and reliable quantitative information, endowing CDs as a universal candidate for a biosensing application by combining target-specific recognition elements.

Chiral recognition of l-amino acids is of significant importance due to the crucial role of l-amino acids in life sciences and pharmaceutics. In this work, a chiral sensor with capability of probing two chiral amino acids by an attractive single-template molecular imprinting strategy is introduced and used in the simultaneous chiral recognition of d/l-alanine (d/l-Ala) and d/l-tyrosine (d/l-Tyr). The assay relies on the hydrolysis of l-alanyl-l-tyrosine dipeptide doped in silica/polypyrrole (SiO 2 /PPy) under acidic conditions, resulting in l-Ala and l-Tyr coimprinted chiral sensor. This work opens up a new avenue for simultaneous chiral sensing of two or more chiral amino acids by incorporating only one template, circumventing the shortcomings encountered with multitemplate molecularly imprinted technology.

In this work, low-power and high-performance gas sensors toward trimethylamine (TMA) are presented for the food quality control in the Internet of Things. An amphiphilic perylene diimide derivative (1,6,7,12-tetra-chlorinated perylene- N-(2-hydroxyethyl)- N'-hexylamine-3,4,9,10-tetracarboxylic bisimide, TC-PDI) is synthesized and further employed to construct the organic microrods of TC-PDI and organic/inorganic microbelts of TC-PDI/CdS by a phase transfer method. Due to the formation of n-n heterojunctions, the TC-PDI/CdS microbelts exhibit higher conductivity than the TC-PDI microrods alone, which present an efficient gas sensing platform for TMA determination at room operating temperature with high reproducibility and selectivity. Remarkably, the limit of detection, stability, and selectivity of the TC-PDI/CdS gas sensor are significantly improved, which ascribes to the efficient charge separation of n-n heterojunctions. More importantly, the fabricated gas sensor provides potential application of "on-site" and "on-line" TMA identification in real systems and suggests an efficient way to develop new hybrid n-n heterojunctions for a low-power and high-performance gas sensor.

Despite the vast time humans spend indoors, indoor air is far less well chemically characterized than the outdoor atmosphere. Advanced instrumentation for measurement of reactive trace gases, particles, and surfaces is enabling a renaissance in indoor chemistry; this Feature highlights the challenges and opportunities for analytical chemistry in the built environment.

Cortisol has been identified as a biomarker in saliva to monitor psychological stress. In this work, we report a label-free paper-based electrical biosensor chip to quantify salivary cortisol at a point-of-care (POC) level. A high specificity of the sensor chip to detect cortisol with a detection limit of 3 pg/mL was achieved by conjugating anticortisol antibody (anti-CAB) on top of gold (Au) microelectrodes using 3,3'-dithiodipropionic acid di(N-hydroxysuccinimide ester (DTSP) as a self-assembled monolayer (SAM) agent. The electrode design utilized poly(styrene)-block-poly(acrylic acid) (PS 67 -b-PAA 27 ) polymer and graphene nanoplatelets (GP) suspension coated on filter paper to increase the sensitivity of the immune response. A biosensor chip was then integrated with a lab-built low-cost miniaturized printed circuit board (PCB) to provide an electrical connection and to wirelessly transmit/receive electrical signals using MATLAB. This fully integrated proposed hand-held device successfully exhibited a wide cortisol-detection range from 3 pg/mL to 10 μg/mL, with a sensitivity of 50 Ω (pg mL -1 ) -1 . The performance of the proposed cortisol sensor chip was validated using an enzyme-linked immunosorbent assay (ELISA) technique with a regression value of 0.9951. The advantages of the newly developed cortisol immune biosensor over previously reported chips include an improved limit of detection, no need for additional redox medium for electron exchange, faster response to achieve stable data, excellent shelf life, and its economical production.

To develop in vivo monitoring meter for pH measurements is still the bottleneck for understanding the role of pH plays in the brain diseases. In this work, a selective and sensitive electrochemical pH meter was developed for real-time ratiometric monitoring of pH in different regions of rat brains upon ischemia. First, 1,2-naphthoquinone (1,2-NQ) was employed and optimized as a selective pH recognition element to establish a 2H(+)/2e(-) approach over a wide range of pH from 5.8 to 8.0. The pH meter demonstrated remarkable selectivity toward pH detection against metal ions, amino acids, reactive oxygen species, and other biological species in the brain. Meanwhile, an inner reference, 6-(ferrocenyl)hexanethiol (FcHT), was selected as a built-in correction to avoid the environmental effect through coimmobilization with 1,2-NQ. In addition, three-dimensional gold nanoleaves were electrodeposited onto the electrode surface to amplify the signal by ∼4.0-fold and the measurement was achieved down to 0.07 pH. Finally, combined with the microelectrode technique, the microelectrochemical pH meter was directly implanted into brain regions including the striatum, hippocampus, and cortex and successfully applied in real-time monitoring of pH values in these regions of brain followed by global cerebral ischemia. The results demonstrated that pH values were estimated to 7.21 ± 0.05, 7.13 ± 0.09, and 7.27 ± 0.06 in the striatum, hippocampus, and cortex in the rat brains, respectively, in normal conditions. However, pH decreased to 6.75 ± 0.07 and 6.52 ± 0.03 in the striatum and hippocampus, upon global cerebral ischemia, while a negligible pH change was obtained in the cortex.

Mass spectrometry is a powerful tool in natural product structure elucidation, but our ability to directly correlate fragmentation spectra to these structures lags far behind similar efforts in peptide sequencing and proteomics. Often, manual data interpretation is required and our knowledge of the expected fragmentation patterns for many scaffolds is limited, further complicating analysis. Here, we summarize advances in natural product structure elucidation based upon the application of collision induced dissociation fragmentation mechanisms.

Although surface-enhanced Raman scattering (SERS) has proven to be an effective tool for label-free monitoring of catalytic reactions, quantitative characterization of reaction kinetics via this technique remains challenging owing to the difficulty in integrating catalytic and plasmonic activities into a single platform. In this work, we report on an easy access to highly sensitive plasmonic nanoarrays for direct and label-free monitoring of a gold-catalyzed reaction by SERS. The hierarchically structured three-dimensional assemblies, which consist of small gold catalyst nanoparticles distributed on a self-assembled monolayer of larger gold nanoparticles, were formed through a simple and rapid stepwise interfacial self-assembling process (fabrication time <10 min). The well-defined interparticle distances (<1 nm) lead to efficient plasmonic coupling and ensure both catalytic and SERS-active sites exposed to the environment. Such a versatile bifunctional platform thus allows quantitative determination of the rate constant and activation energy of the catalytic reaction with SERS.

Ion-selective electrodes (ISEs) containing neutral ionophores are used in clinical, industrial, and environmental analysis. The wide range of applications requires deep theoretical description. This work concentrates on the development of the general approach to the description of electro-diffusion processes, namely, Nernst-Planck-Poisson (NPP) model to allow the description of the time-dependent responses in the case of complexation reactions occurring in the ion-selective membranes. The impact of the chemical reaction on the calibration curves and apparent selectivity of ISE is discussed. Results obtained using NPP model with time-dependent reaction are compared with those obtained with the Phase Boundary Model (PBM), as well as with the previous solutions of NPP model, using the infinite reaction rates and constant ligand concentration assumption. The validity of these assumptions is investigated and the limitations of PBM in the description of neutral-carrier ISE are discussed.

In this work, a routinely applicable approach is presented to characterize metal NPs. Individual droplets generated from a microdroplet generator (MDG) were merged into an aerosol generated by a pneumatic nebulizer (PN) and introduced into an ICPMS. The MDG offers high transport efficiency of individual and discrete droplets and was therefore used to establish a calibration function for mass quantification of NPs which were introduced through the PN following the single particle procedure as described elsewhere. The major advantages of such a combined configuration include fast processing of large sample volumes, fast exchanges of different sample matrixes, and the calibration of the NP signal using traceable elemental standards, thus avoiding the need to use NP reference materials or other, not always thoroughly characterized, commercially available NPs. The transport efficiency of the sample introduction is calculated based on the fact that 100% of the calibrant reaches the plasma through the MDG, whereas for the PN a NP suspension containing a known number concentration is used. Alternatively, bulk analysis of the NP material allows transport efficiency determination without any additional information from reference NPs. With this method, we could determine the size of standard silver NPs at 60.4 ± 1.0 nm and 80.0 ± 1.4 nm, respectively, which agrees with the size ranges given by the supplier (60.8 ± 6.6 nm and 79.8 ± 5.4 nm). Furthermore, we were also able to determine the NPs number concentration of the sample (Ag/Au) with a deviation of 3.2% the expected value.

Accurate, reproducible, and fast quantification of N-glycans is crucial not only for the development and quality control of modern glycosylated biopharmaceuticals, but also in clinical biomarker discovery. Several methods exist for fluorescent labeling of N-glycans and subsequent chromatographic separation and quantification. However, the methods can be complex, lengthy, and expensive. Here we report an automated ultrafiltration-based N-glycoanalytical workflow combined with a glycan labeling strategy that is based on the reaction of glycosylamines with fluorescent carbamate. The entire protocol is quick, simple, and cost-effective and requires less than 1 μg of protein per sample. As many as 768 affinity purified IgG glycoprotein samples can be prepared in a single run with a liquid handling platform.

Protein A is often used for the purification and detection of antibodies such as immunoglobulin G (IgG) because of its quadrivalent domains that bind to the Fc region of these macromolecules. However, the kinetics and thermodynamics of the binding to many sensor surfaces have eluded mechanistic description due to complexities associated with multivalent interactions. In this work, we use a near-infrared (nIR) fluorescent single-walled carbon nanotube sensor array to obtain the kinetics of IgG binding to protein A, immobilized using a chelated Cu(2+)/His-tag chemistry to hydrogel dispersed sensors. A bivalent binding mechanism is able to describe the concentration dependence of the effective dissociation constant, KD,eff, which varies from 100 pM to 1 μM for IgG concentrations from 1 ng mL(-1) to 100 μg mL(-1), respectively. The mechanism is shown to describe the unusual concentration-dependent scaling demonstrated by other sensor platforms in the literature as well, and a comparison is made between resulting parameters. For comparison, we contrast IgG binding with that of human growth hormone (hGH) to its receptor (hGH-R) which displays an invariant dissociation constant at KD = 9 μM. These results should aid in the use of protein A and other recognition elements in a variety of sensor types.

Herein, it is the first report that a cathodic electrochemiluminescence (ECL) resonance energy transfer (ERET) system is fabricated by layer-by-layer (LBL) electrostatic assembly of CoAl layered double hydroxide (LDH) nanosheets with a mixture of blue BSA-gold nanoclusters (AuNCs) and Ru(bpy)3(2+) (denoted as AuNCs@Ru) on an Au electrode. The possible ECL mechanism indicates that the appearance of CoAl-LDH nanosheets generates a long-range stacking order of the AuNCs@Ru on an Au electrode, facilitating the occurrence of the ERET between BSA-AuNC donors and Ru(bpy)3(2+) acceptors on the as-prepared AuNCs@Ru-LDH ultrathin films (UTFs). Furthermore, it is observed that the cathodic ECL intensity can be quenched efficiently in the presence of 6-mercaptopurine (6-MP) in a linear range of 2.5-100 nM with a detection limit of 1.0 nM. On the basis of these interesting phenomena, a facile cathodic ECL sensor has successfully distinguished 6-MP from other thiol-containing compounds (e.g., cysteine and glutathione) in human serum and urine samples. The proposed sensing scheme opens a way for employing the layered UTFs as a platform for the cathodic ECL of Ru(bpy)3(2+).

In the present work, three-dimensional porous HxTiS2 nanosheet-polyaniline (PANI) nanocomposites were first synthesized by a two-step method. First, HxTiS2 ultrathin nanosheets were prepared by the lithium intercalation and exfoliation method, followed by the surface polymerization reactions of aniline. The influences of the amount of HxTiS2 nanosheets on the nanocomposite morphology and electrochemical performances of the nanocomposites modified glass carbon electrode (HxTiS2 nanosheet-PANI/GCE) were investigated. The results demonstrated that the incorporation of HxTiS2 nanosheets as a suitable substrate can regulate the growth of PANI, enhance the electrode stability and improve interfacial electron transfer rates. In addition, based on the nanocomposites, we developed a novel electrochemical sensor to directly detect trace Cu(2+), and discovered that the coordination interaction between Cu(2+) cations and the N atoms of the imine moieties in PANI endowed the electrochemical sensor with high selectivity. Because of the synergetic effects of HxTiS2 nanosheets and PANI, the as-prepared electrochemical sensor exhibited highly sensitive and selective assaying of Cu(2+) with a detection limit of 0.7 nM (signal-to-noise ratio (S/N) equal to 3) and a linear range from 25 nM to 5 μM, under optimal conditions.

A gas-cylinder-free plasma desorption/ionization system was developed to realize a mobile on-site analytical device for detection of chemical warfare agents (CWAs). In this system, the plasma source was directly connected to the inlet of a mass spectrometer. The plasma can be generated with ambient air, which is drawn into the discharge region by negative pressure in the mass spectrometer. High-power density pulsed plasma of 100 kW could be generated by using a microhollow cathode and a laboratory-built high-intensity pulsed power supply (pulse width: 10-20 μs; repetition frequency: 50 Hz). CWAs were desorbed and protonated in the enclosed space adjacent to the plasma source. Protonated sample molecules were introduced to the mass spectrometer by airflow through the discharge region. To evaluate the analytical performance of this device, helium and air plasma were directly irradiated to CWAs in the gas-cylinder-free plasma desorption/ionization system and the protonated molecules were analyzed by using an ion-trap mass spectrometer. A blister agent (nitrogen mustard 3) and nerve gases [cyclohexylsarin (GF), tabun (GA), and O-ethyl S-2-N,N-diisopropylaminoethyl methylphosphonothiolate (VX)] in solution in n-hexane were applied to the Teflon rod and used as test samples, after solvent evaporation. As a result, protonated molecules of CWAs were successfully observed as the characteristic ion peaks at m/z 204, 181, 163, and 268, respectively. In air plasma, the limits of detection were estimated to be 22, 20, 4.8, and 1.0 pmol, respectively, which were lower than those obtained with helium plasma. To achieve quantitative analysis, calibration curves were made by using CWA stimulant dipinacolyl methylphosphonate as an internal standard; straight correlation lines (R(2) = 0.9998) of the peak intensity ratios (target per internal standard) were obtained. Remarkably, GA and GF gave protonated dimer ions, and the ratios of the protonated dimer ions to the protonated monomers increased with the amount of GA and GF applied.

We demonstrate the combination of the time-resolved fluorescence resonance energy transfer (tr-FRET) measurement and the ultrarapid hydrodynamic focusing microfluidic mixer. The combined technique is capable of probing the intermolecular distance change with temporal resolution at microsecond level and structural resolution at Angstrom level, and the use of two-photon excitation enables a broader exploration of FRET with spectrum from near-ultraviolet to visible wavelength. As a proof of principle, we used the coupled microfluidic laminar flow and time-resolved two-photon excitation microscopy to investigate the early folding states of Cytochrome c (cyt c) by monitoring the distance between the tryptophan (Trp-59)-heme donor-acceptor (D-A) pair. The transformation of folding states of cyt c in the early 500 μs of refolding was revealed on the microsecond time scale. For the first time, we clearly resolved the early transient state of cyt c, which is populated within the dead time of the mixer (<10 μs) and has a characteristic Trp-59-heme distance of ∼31 Å. We believe this tool can find more applications in studying the early stages of biological processes with FRET as the probe.

In order to investigate the incorporation of drugs into hair, matrix-assisted laser desorption/ionization-time-of-flight tandem mass spectrometry (MS/MS) imaging was performed on the longitudinal sections of single scalp hair shafts sampled from volunteers after a single oral administration of methoxyphenamine (MOP), a noncontrolled analogue of methamphetamine. Hair specimens were collected by plucking out with the roots intact, and these specimens were prepped by an optimized procedure based on freeze-sectioning to detect the drug inside the hair shaft and hair root. Time-course changes in the imaging results, with confirmatory quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for each 1-mm segment of single hair strands, revealed a substantial concentration of the drug first onto the hair bulbs after ingestion, while only a small portion appeared to be incorporated into the hair matrix, forming a 2-3 mm distinctive drug band with tailing. Comparable amount of the drug also appeared to be incorporated into the keratinized hair shaft in the upper dermis zone, forming another distinct drug band of about 2 mm, which both moved toward the distal side, following the strand's growth rate. These findings provide forensically crucial information: there are two major drug incorporation sites, at least for MOP, which cause overlap of the recordings and deteriorates its chronological resolution down to about 11 days or perhaps longer.

Simultaneous discriminative sensing of biothiols in vitro and in living cells has remained challenging. Herein, we report a new sulfonamide-based self-quenched fluorescent probe 1 for this purpose with high sensitivity and good selectivity. Treatment of 1 with cysteine (Cys), homocysteine (Hcy), or glutathione (GSH) yields aminoluciferin, 2-cyano-6-aminobenzothiazole homocysteine (CBTHcy), or 2-cyano-6-aminobenzothiazole (CBT), turning "on" the fluorescence at wavelengths of 522, 517, or 490 nm, respectively. Kinetic study indicated that 1 reacts with Cys faster than with Hcy or GSH. With these unique properties of 1, we applied 1 for highly sensitive sensing of Cys, Hcy, and GSH among other 19 natural amino acids (AAs) with good selectivity. Confocal fluorescence microscopic imaging of 1-treated HepG2 cells at two channels (522 ± 8 and 490 ± 8 nm), together with quantitative analysis, indicated that the "turn-on" fluorescence was induced by intracellular Cys-dominating condensation and reduction of 1 but not by intracellular GSH-dominating reduction of 1. This suggests that 1 could be applied for discriminative sensing of intracellular Cys from the abundant GSH. Further development of 1 might bring about an efficient tool for probing cellular functions that relate to biothiols.

A novel iridium(III) complex-based probe Ir4-1 has been designed and synthesized conveniently by incorporating the chemodosimeter into phosphorescent luminophor, which displayed ratiometric luminescence change from yellowish-green to reddish-yellow only toward Hg(2+) ions in aqueous media via desulfurization and intramolecular cyclization with a broad pH range of 5-10. The phosphorescent chemodosimeter could eliminate effectively the signal interference from the short-lived fluorescent background, and the signal-to-noise ratio of the detection was improved distinctly by using time-resolved photoluminescence technique. Furthermore, the mechanism of phosphoresce change of the chemodosimeter was analyzed in detail by time-dependent density functional theory (TD-DFT) calculations, and the probe with long-wavelength emission could be applied to label cells and monitor intracellular Hg(2+) effectively by luminescence ratio imaging.

We review recent progress in the development of two-dimensional (2-D) photonic crystal (PC) materials for chemical and biological sensing applications. Self-assembly methods were developed in our laboratory to fabricate 2-D particle array monolayers on mercury and water surfaces. These hexagonal arrays strongly forward Bragg diffract light to report on their array spacings. By embedding these 2-D arrays onto responsive hydrogel surfaces, 2-D PC sensing materials can be fabricated. The 2-D PC sensors utilize responsive polymer hydrogels that are chemically functionalized to show volume phase transitions in selective response to particular chemical species. Novel hydrogels were also developed in our laboratory by cross-linking proteins while preserving their native structures to maintain their selective binding affinities. The volume phase transitions swell or shrink the hydrogels, which alter their 2-D array spacings, and shift their diffraction wavelengths. These shifts can be visually detected or spectrally measured. These 2-D PC sensing materials have been used for the detection of many analytes, such as pH, surfactants, metal ions, proteins, anionic drugs, and ammonia. We are exploring the use of organogels that use low vapor pressure ionic liquids as their mobile phases for sensing atmospheric analytes.

In this paper we describe the development of a 5 mm NMR flow tube that can be used in a standard 5 mm NMR probe, enabling the user to conduct experiments on flowing samples or, more specifically, on flowing reaction mixtures. This enables reaction monitoring or kinetic experiments to be conducted by flowing reaction mixtures from a reaction vessel to detection in the coil area of the NMR, without the need for a specialized flow NMR probe. One of the key benefits of this flow tube is that it provides flexibility to be used across a range of available spectrometers of varying magnetic field strengths with a standard 5 mm probe setup. The applicability of this flow tube to reaction monitoring is demonstrated using the reaction of p-phenylenediamine and isobutyraldehyde to form the diimine product.

A new analytical system based on Thermochromic Etching Discs (TED) technology is presented. TED comprises a number of attractive features such as track independency, selective irradiation, a high power laser, and the capability to create useful assay platforms. The analytical versatility of this tool opens up a wide range of possibilities to design new compact disc-based total analysis systems applicable in chemistry and life sciences. In this paper, TED analytical implementation is described and discussed, and their analytical potential is supported by several applications. Microarray immunoassay, immunofiltration assay, solution measurement, and cell culture approaches are herein addressed in order to demonstrate the practical capacity of this system. The analytical usefulness of TED technology is herein demonstrated, describing how to exploit this tool for developing truly integrated analytical systems that provide solutions within the point of care framework.

Localized surface plasmon resonance (LSPR) represents a sensitive and versatile method for detection of biomolecules in a label-free fashion, but identification of bound analytes can be challenging with LSPR alone, especially for samples in a complex medium. We report the fabrication of an optically active, plasmonic film of gold nanoparticles by using a self-assembly and calcination process, which offers orthogonal measurements enabling multifaceted characterization on the same surface with LSPR and surface-assisted laser desorption/ionization mass spectrometry. This proof-of-concept study involves plasmonic characterization of the fabricated nanofilm, real-time monitoring of vesicle-surface interactions toward formation of fluid lipid bilayer, and mass spectrometric analysis of peptides and cytochrome c digest. This multifunction-enabling surface material can yield complementary analytical information, providing new tools for comprehensive analysis of biomolecular samples.

The feasibility of using smartphones and other mobile devices as the detection platform for quantitative scanometric assays is demonstrated. The different scanning modes (color, grayscale, black/white) and grayscale converting protocols (average, weighted average/luminosity, and software specific) have been compared in determining the optical darkness ratio (ODR) values, a conventional quantitation measure for scanometric assays. A mobile app was developed to image and analyze scanometric assays, as demonstrated by paper-printed tests and a biotin-streptavidin assay on a plastic substrate. Primarily for ODR analysis, the app has been shown to perform as well as a traditional desktop scanner, augmenting that smartphones (and other mobile devices) promise to be a practical platform for accurate, quantitative chemical analysis and medical diagnostics.

Fourier transform (FT)-plasmon waveguide resonance (PWR) spectroscopy measures light reflectivity at a waveguide interface as the incident frequency and angle are scanned. Under conditions of total internal reflection, the reflected light intensity is attenuated when the incident frequency and angle satisfy conditions for exciting surface plasmon modes in the metal as well as guided modes within the waveguide. Expanding upon the concept of two-frequency surface plasmon resonance developed by Peterlinz and Georgiadis [Opt. Commun. 1996, 130, 260], the apparent index of refraction and the thickness of a waveguide can be measured precisely and simultaneously by FT-PWR with an average percent relative error of 0.4%. Measuring reflectivity for a range of frequencies extends the analysis to a wide variety of sample compositions and thicknesses since frequencies with the maximum attenuation can be selected to optimize the analysis. Additionally, the ability to measure reflectivity curves with both p- and s-polarized light provides anisotropic indices of refraction. FT-PWR is demonstrated using polystyrene waveguides of varying thickness, and the validity of FT-PWR measurements are verified by comparing the results to data from profilometry and atomic force microscopy (AFM).

The development of a portable and easy-to-use device for the detection of explosives with high sensitivity and selectivity is in high demand for homeland security and public safety. In this study, we demonstrate miniaturized devices depending on the upconversion ratiometric luminescent probe for point-of-care (POC) assay of explosives with the naked-eye. When the PEI-coated upconversion nanoparticles (UCNPs) selectively bonded to 2,4,6-trinitrotoluene (TNT) explosives by the formation of Meisenheimer complex, the formed of UCNP-Meisenheimer complexes show turned visible multicolor upconversion luminescence (UCL) on account of TNT-modulating Förster resonance energy transfer process under near-infrared excitation. With UCL emission at 808 nm as internal standard and ratiometric UCL at 477 nm to that at 808 nm (I477/I808) as output signal, the probe can simultaneously meet the accuracy for TNT explosives quantitative analysis. In addition, this easy-to-use visual technique provides a powerful tool for convenient POC assay of rapid explosives identification.

Paper-based diagnostic assays are gaining increasing popularity for their potential application in resource-limited settings and for point-of-care screening. Achievement of high sensitivity with precision and accuracy can be challenging when using paper substrates. Herein, we implement the red-green-blue color palette of a digital camera for quantitative ratiometric transduction of nucleic acid hybridization on a paper-based platform using immobilized quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET). A nonenzymatic and reagentless means of signal enhancement for QD-FRET assays on paper substrates is based on the use of dry paper substrates for data acquisition. This approach offered at least a 10-fold higher assay sensitivity and at least a 10-fold lower limit of detection (LOD) as compared to hydrated paper substrates. The surface of paper was modified with imidazole groups to assemble a transduction interface that consisted of immobilized QD-probe oligonucleotide conjugates. Green-emitting QDs (gQDs) served as donors with Cy3 as an acceptor. A hybridization event that brought the Cy3 acceptor dye in close proximity to the surface of immobilized gQDs was responsible for a FRET-sensitized emission from the acceptor dye, which served as an analytical signal. A hand-held UV lamp was used as an excitation source and ratiometric analysis using an iPad camera was possible by a relative intensity analysis of the red (Cy3 photoluminescence (PL)) and green (gQD PL) color channels of the digital camera. For digital imaging using an iPad camera, the LOD of the assay in a sandwich format was 450 fmol with a dynamic range spanning 2 orders of magnitude, while an epifluorescence microscope detection platform offered a LOD of 30 fmol and a dynamic range spanning 3 orders of magnitude. The selectivity of the hybridization assay was demonstrated by detection of a single nucleotide polymorphism at a contrast ratio of 60:1. This work provides an important framework for the integration of QD-FRET methods with digital imaging for a ratiometric transduction of nucleic acid hybridization on a paper-based platform.

Dietary antioxidants as health promoters for human beings have attracted much attention and triggered tremendous efforts in evaluation of the antioxidant capacity. Unfortunately, no versatile detection system has been designed to date. Due to the possible synergistic effect among antioxidant components in a diversified system, to isolate and quantify an individual antioxidant via a chromatography approach limits the scope for global antioxidant activity assay. Quality inspections with a spectroscopy strategy to any colored food are far from satisfactory. Herein, a photoelectrochemical (PEC) platform with an ultrasensitive titanium dioxide decorated sulfonated graphene (SGE-TiO2) based transducer was introduced for antioxidant monitoring. Under an open circuit potential (zero potential), with extraordinary response, excellent reproducibility and stability, this PEC sensor could be successfully applied for rational analysis of the global antioxidant capacity. Such a highly efficient strategy showed advantages such as simplicity, convenience, high sensitivity and universality, which were also applicable to the detection of colored system. Moreover, the PEC sensor could be employed for practical evaluation of antioxidant capacity of teas. The concerned mechanism was further proposed and adequately discussed. This straightforward yet powerful approach provides a general format for dietary antioxidant assessment in foodstuff industries.

This work describes the method of a selective hydride generation-cryotrapping (HG-CT) coupled to an extremely sensitive but simple in-house assembled and designed atomic fluorescence spectrometry (AFS) instrument for determination of toxicologically important As species. Here, an advanced flame-in-gas-shield atomizer (FIGS) was interfaced to HG-CT and its performance was compared to a standard miniature diffusion flame (MDF) atomizer. A significant improvement both in sensitivity and baseline noise was found that was reflected in improved (4 times) limits of detection (LODs). The yielded LODs with the FIGS atomizer were 0.44, 0.74, 0.15, 0.17 and 0.67 ng L(-1) for arsenite, total inorganic, mono-, dimethylated As and trimethylarsine oxide, respectively. Moreover, the sensitivities with FIGS and MDF were equal for all As species, allowing for the possibility of single species standardization with arsenate standard for accurate quantification of all other As species. The accuracy of HG-CT-AFS with FIGS was verified by speciation analysis in two samples of bottled drinking water and certified reference materials, NRC CASS-5 (nearshore seawater) and SLRS-5 (river water) that contain traces of methylated As species. As speciation was in agreement with results previously reported and sums of all quantified species corresponded with the certified total As. The feasibility of HG-CT-AFS with FIGS was also demonstrated by the speciation analysis in microsamples of exfoliated bladder epithelial cells isolated from human urine. The results for the sums of trivalent and pentavalent As species corresponded well with the reference results obtained by HG-CT-ICPMS (inductively coupled plasma mass spectrometry).

We report a newly developed technique for the in situ real-time gas analysis of reactors commonly used for the production of nanomaterials, by showing case-study results obtained using a dedicated apparatus for measuring the gas composition in reactors operating at high temperature (<1000 °C). The in situ gas-cooled sampling probe mapped the chemistry inside the high-temperature reactor, while suppressing the thermal decomposition of the analytes. It thus allows a more accurate study of the mechanism of progressive thermocatalytic cracking of precursors compared to previously reported conventional residual gas analyses of the reactor exhaust gas and hence paves the way for the controlled production of novel nanomaterials with tailored properties. Our studies demonstrate that the composition of the precursors dynamically changes as they travel inside of the reactor, causing a nonuniform growth of nanomaterials. Moreover, mapping of the nanomaterials reactor using quantitative gas analysis revealed the actual contribution of thermocatalytic cracking and a quantification of individual precursor fragments. This information is particularly important for quality control of the produced nanomaterials and for the recycling of exhaust residues, ultimately leading toward a more cost-effective continuous production of nanomaterials in large quantities. Our case study of multiwall carbon nanotube synthesis was conducted using the probe in conjunction with chemical vapor deposition (CVD) techniques. Given the similarities of this particular CVD setup to other CVD reactors and high-temperature setups generally used for nanomaterials synthesis, the concept and methodology of in situ gas analysis presented here does also apply to other systems, making it a versatile and widely applicable method across a wide range of materials/manufacturing methods, catalysis, as well as reactor design and engineering.

A simple molecular fluorescent probe 5 has been designed and synthesized by appending anthracene and benzhydryl moieties through a piperazine bridge. The probe upon interaction with different metal ions showed high selectivity and sensitivity (2 ppb) for Hg(2+) through fluorescence "turn-on" response in HEPES buffer. The significant fluorescence enhancement (~10-fold) is attributable to PET arrest due to complexation with nitrogen atoms of the piperazine unit and Hg(2+) in 1:2 stoichiometry, in which a naked-eye sensitive fluorescent blue color of solution changed to a blue-green (switched-on). As a proof of concept, promising prospects for application in environmental and biological sciences 5 have been utilized to detect Hg(2+) sensitively in real samples, on cellulose paper strips, in protein medium (like BSA), and intracellularly in HeLa cells. Moreover, the optical behavior of 5 upon providing different chemical inputs has been utilized to construct individual logic gates and a reusable combinational logic circuit. The combinational circuit (switch ON mode; OR logic gate) is easily resettable to the original position (switch OFF mode; INHIBIT logic gate) by applying reset chemical inputs (OH(-) and PO4(3-)) with great reproducibility.

Protein stable isotope fingerprinting (P-SIF) is a method to measure the carbon isotope ratios of whole proteins separated from complex mixtures, including cultures and environmental samples. The goal of P-SIF is to expose the links between taxonomic identity and metabolic function in microbial ecosystems. To accomplish this, two dimensions of chromatography are used in sequence to resolve a sample containing ca. 5-10 mg of mixed proteins into 960 fractions. Each fraction then is split in two aliquots: The first is digested with trypsin for peptide sequencing, while the second has its ratio of (13)C/(12)C (value of δ(13)C) measured in triplicate using an isotope-ratio mass spectrometer interfaced with a spooling wire microcombustion device. Data from cultured species show that bacteria have a narrow distribution of protein δ(13)C values within individual taxa (±0.7-1.2‰, 1σ). This is moderately larger than the mean precision of the triplicate isotope measurements (±0.5‰, 1σ) and may reflect heterogeneous distribution of (13)C among the amino acids. When cells from different species are mixed together prior to protein extraction and separation, the results can predict accurately (to within ±1σ) the δ(13)C values of the original taxa. The number of data points required for this endmember prediction is ≥20/taxon, yielding a theoretical resolution of ca. 10 taxonomic units/sample. Such resolution should be useful to determine the overall trophic breadth of mixed microbial ecosystems. Although we utilize P-SIF to measure natural isotope ratios, it also could be combined with experiments that incorporate stable isotope labeling.

Ion selective optical sensors are typically interrogated under conditions where the sample concentration is not altered during measurement. We describe here an alternative exhaustive detection mode for ion selective optical sensors. This exhaustive sensor concept is demonstrated with ionophore-based nanooptodes either selective for calcium or the polycationic heparin antidote protamine. In agreement with a theoretical treatment presented here, linear calibration curves were obtained in the exhaustive detection mode instead of the sigmoidal curves for equilibrium-based sensors. The response range can be tuned by adjusting the nanosensor loading. The nanosensors showed average diameters of below 100 nm and the sensor response was found to be dramatically faster than that for film-based optodes. Due to the strong binding affinity of the exhaustive nanosensors, total calcium concentration in human blood plasma was successfully determined. Optical determination of protamine in human blood plasma using the exhaustive nanosensors was attempted, but was found to be less successful.

An "off-on" electrochemiluminescence (ECL) strategy was constructed for highly sensitive and selective detection of adenosine 5'-triphosphate (ATP) with a quantum dots (QDs) modified electrode and a DNAzyme signal probe. The immobilized QDs were functionalized with a DNA sequence (DNA1) and then aptamer for recognition of target analyte. The signal probe was prepared by assembling another DNA sequence (DNA2) and G-quadruplex on gold nanoparticle via Au-S chemistry, which was used to bind the probe to electrode surface through a hybridization reaction with aptamer and hemin for forming G-quadruplex/hemin DNAzyme, respectively. Upon the sandwich hybridization of DNA1-aptamer-DNA2, the signal probe could be captured on the aptasensor to catalyze the reduction of dissolved oxygen, the coreactant for cathodic ECL emission of QDs, leading to a decrease of ECL intensity and thus the "off" state. In the presence of target, its recognition by aptamer led to the release of aptamer from electrode surface and decreased the amount of captured signal probe, thus the ECL emission was in its "on" state. The "off-on" strategy resulted from the target-induced structure switching could be used for specific detection of ATP with a linear range of 8-2000 nM and a detection limit of 7.6 nM. The proposed aptasensor could be successfully applied in the ECL detection of ATP in human serum. This method could resist environmental interfering agents and be extended for sensitive and reliable detection of a wide range of analytes in complex sample.

The development of probes for rapid, selective, and sensitive detection of the highly toxic thiophenols is of great importance in both environmental and biological science. Despite the appealing advantages of near-infrared (NIR) fluorescent detection, no NIR fluorescent probes have been reported for thiophenols to date. Using the chemical properties of thiophenols that are able to cleave sulfonamide selectively and efficiently under mild conditions, we herein report a dicyanomethylene-benzopyran (DCMB)-based NIR fluorescent probe for thiophenols. This probe features remarkable large Stokes shift and shows a rapid, highly selective, and sensitive detection process for thiophenols with significant NIR fluorescent turn-on responses. The potential applications of this new NIR fluorescent probe were demonstrated by the quantitative detection of thiophenol in real water samples and by fluorescent imaging of thiophenol in living cells.

We demonstrate the first use of smartphone spectrophotometry for readout of fluorescence-based biological assays. We evaluated the smartphone fluorimeter in the context of a fluorescent molecular beacon (MB) assay for detection of specific nucleic acid sequences in a liquid test sample and compared performance against a conventional laboratory fluorimeter. The capability of distinguishing a one-point mismatch is also demonstrated by detecting single-base mutation in target nucleic acids. Our approach offers a route toward portable biomolecular assays for viral/bacterial pathogens, disease biomarkers, and toxins.

Carbon nanotube (CNT)-based microelectrodes have been investigated as alternatives to carbon-fiber microelectrodes for the detection of neurotransmitters because they are sensitive, exhibit fast electron transfer kinetics, and are more resistant to surface fouling. Wet spinning CNTs into fibers using a coagulating polymer produces a thin, uniform fiber that can be fabricated into an electrode. CNT fibers formed in poly(vinyl alcohol) (PVA) have been used as microelectrodes to detect dopamine, serotonin, and hydrogen peroxide. In this study, we characterize microelectrodes with CNT fibers made in polyethylenimine (PEI), which have much higher conductivity than PVA-CNT fibers. PEI-CNT fibers have lower overpotentials and higher sensitivities than PVA-CNT fiber microelectrodes, with a limit of detection of 5 nM for dopamine. The currents for dopamine were adsorption controlled at PEI-CNT fiber microelectrodes, independent of scan repetition frequency, and stable for over 10 h. PEI-CNT fiber microelectrodes were resistant to surface fouling by serotonin and the metabolite interferant 5-hydroxyindoleacetic acid (5-HIAA). No change in sensitivity was observed for detection of serotonin after 30 flow injection experiments or after 2 h in 5-HIAA for PEI-CNT electrodes. The antifouling properties were maintained in brain slices when serotonin was exogenously applied multiple times or after bathing the slice in 5-HIAA. Thus, PEI-CNT fiber electrodes could be useful for the in vivo monitoring of neurochemicals.

Herein, a small-molecule fluorescent sensor array for rapid identification of seven heavy metal ions was designed and synthesized, with its sensing mechanism mimicking that of a tongue. The photoinduced electron transfer and intramolecular charge transfer mechanism result in combinatorial interactions between sensor array and heavy metal ions, which lead to diversified fluorescence wavelength shifts and emission intensity changes. Upon principle component analysis (PCA), this result renders clear identification of each heavy metal ion on a 3D spatial dispersion graph. Further exploration provides a concentration-dependent pattern, allowing both qualitative and quantitative measurements of heavy metal ions. On the basis of this information, a "safe-zone" concept was proposed, which provides rapid exclusion of versatile hazardous species from clean water samples based on toxicity characteristic leaching procedure standards. This type of small-molecule fluorescent sensor array could open a new avenue for multiple heavy metal ion detection and simplified water quality analysis.

Environmentally responsive polymers are becoming increasingly important in the biomaterials field for use as diagnostic reagents, drug carriers, and tissue engineering scaffolds. Characterizing polymer phase transitions by cloud point curves typically requires large milliliter volumes of sample at high micromolar solution concentrations. Here we present a method based on quantification of thermophoretic Soret diffusion that allows determination of polymer phase transitions using only ~1 μL of liquid at dilute nanomolar concentrations, effectively reducing the amount of sample required by a factor of 10(6). We prepared an oligo(ethylene glycol) (OEG) methyl ether methacrylate copolymer via RAFT polymerization. End-group modification with fluorescent BODIPY-maleimide provided a dye-labeled pOEG-BODIPY conjugate with a lower critical solution temperature (LCST) in the range of ~25-35 °C. Thermophoresis measurements in dilute solution demonstrated a marked change in polymer thermodiffusion in the vicinity of the LCST. We measured the temperature dependence of thermodiffusion and transformed these data sets into sigmoidal curves characterizing the phase transition of the polymer. Finite element modeling suggested a correction to the measured values that brought the transition temperatures measured by thermophoresis into accord with the cloud point curves. Our results demonstrate that observation of polymer thermodiffusion in a low volume dilute format is a facile method for determining polymer phase transition temperatures.

As a cheap and abundant porous material, cellulose filter paper was used to immobilize nano-TiO2 and denoted as TiO2/cellulose paper (TCP). With high adsorption capacity for Cu(II) (more than 1.65 mg), TCP was used as an adsorbent, photocatalyst, and colorimetric sensor at the same time. Under the optimum adsorption conditions, i.e., pH 6.5 and 25 °C, the adsorption ratio of Cu(II) was higher than 96.1%. Humic substances from the matrix could be enriched onto TCP but the interference of their colors on colorimetric detection could be eliminated by the photodegradation. In the presence of hydroxylamine, neocuproine, as a selective indicator, was added onto TCP, and a visual color change from white to orange was generated. The concentration of Cu(II) was quantified by the color intensity images using image processing software. This fully integrated visual analysis system was successfully applied for the detection of Cu(II) in 10.0 L of drinking water and seawater with a preconcentration factor of 10(4). The log-linear calibration curve for Cu(II) was in the range of 0.5-50.0 μg L(-1) with a determination coefficient (R(2)) of 0.985 and its detection limit was 0.073 μg L(-1).

An approach for sensitive magnetic resonance detection of metal cations is proposed. Combining the use of hyperpolarized (129)Xe NMR and of a cage-molecule functionalized by a ligand able to chelate different cations, we show that simultaneous detection of lead, zinc, and cadmium ions at nanomolar concentration is possible in short time, thanks to fast MRI sequences based on the HyperCEST scheme.

Although commonly known as a highly toxic chemical, cyanide is also an essential reagent for many industrial processes in areas such as mining, electroplating, and synthetic fiber production. The "heavy" use of cyanide in these industries, along with its necessary transportation, increases the possibility of human exposure. Because the onset of cyanide toxicity is fast, a rapid, sensitive, and accurate method for the diagnosis of cyanide exposure is necessary. Therefore, a field sensor for the diagnosis of cyanide exposure was developed based on the reaction of naphthalene dialdehyde, taurine, and cyanide, yielding a fluorescent β-isoindole. An integrated cyanide capture "apparatus", consisting of sample and cyanide capture chambers, allowed rapid separation of cyanide from blood samples. Rabbit whole blood was added to the sample chamber, acidified, and the HCN gas evolved was actively transferred through a stainless steel channel to the capture chamber containing a basic solution of naphthalene dialdehyde (NDA) and taurine. The overall analysis time (including the addition of the sample) was <3 min, the linear range was 3.13-200 μM, and the limit of detection was 0.78 μM. None of the potential interferents investigated (NaHS, NH4OH, NaSCN, and human serum albumin) produced a signal that could be interpreted as a false positive or a false negative for cyanide exposure. Most importantly, the sensor was 100% accurate in diagnosing cyanide poisoning for acutely exposed rabbits.

A novel sulfonamide-conjugated benzo-[2,1-b:3,4-b']bithiophene semiconductor has been designed and synthetized in order to develop a probe for specific detection of anions both in the homogeneous (solution) and heterogeneous phase. Its photophysical and electrochemical data were reported in this study. On the basis of the optical and NMR titrations analysis, the chelator was found to be highly selective for fluoride compared to others anions (Ka = 1.6 × 10(4) M(-1) in dimethyl sulfoxide (DMSO)). In addition, from an intricate sample, the novel chelator shows exceptional specificity toward fluoride and reveals a complete reversibility after addition of trifluoroacetic acid (TFA). Sensing films were obtained by electrochemical polymerization of the probe on an electrode surface, which clearly show effective detection of fluoride.

We demonstrate the hybridization-induced fluorescence detection of DNA on an origami-based paper analytical device (oPAD). The paper substrate was patterned by wax printing and controlled heating to construct hydrophilic channels and hydrophobic barriers in a three-dimensional fashion. A competitive assay was developed where the analyte, a single-stranded DNA (ssDNA), and a quencher-labeled ssDNA competed for hybridization with a fluorophore-labeled ssDNA probe. Upon hybridization of the analyte with the fluorophore-labeled ssDNA, a linear response of fluorescence vs analyte concentration was observed with an extrapolated limit of detection <5 nM and a sensitivity relative standard deviation as low as 3%. The oPAD setup was also tested against OR/AND logic gates, proving to be successful in both detection systems.

Functionalized single-walled carbon nanotube (SWCNT)-based chemiresistors are reported for a highly robust and sensitive gas sensor to selectively detect cyclohexanone, a target analyte for explosive detection. The trifunctional selector has three important properties: it noncovalently functionalizes SWCNTs with cofacial π-π interactions, it binds to cyclohexanone via hydrogen bond (mechanistic studies were investigated), and it improves the overall robustness of SWCNT-based chemiresistors (e.g., humidity and heat). Our sensors produced reversible and reproducible responses in less than 30 s to 10 ppm of cyclohexanone and displayed an average theoretical limit of detection (LOD) of 5 ppm.

In this paper, the anodic electrogenerated chemiluminescence (ECL) behavior of graphite-like carbon nitride (g-C3N4) is studied using cyclic voltammetry with triethanolamine (TEA) as a coreactant. The possible anodic ECL response mechanism of the g-C3N4/TEA system is proposed. Furthermore, it is observed that the anodic ECL signal can be quenched efficiently in the presence of rutin, on the basis of which a facile anodic ECL senor for the determination of rutin is developed. This ECL sensor is found to have a linear response in the range of 0.20-45.0 μM and a low detection limit of 0.14 μM (at signal-to-noise of 3). These results suggest that semiconductor g-C3N4 has great potential in extending the application in the ECL field as an efficient luminophore.

A new molecularly imprinted electrochemical luminescence (MIP-ECL) sensor was developed for Gibberellin A3 (GA3) determination. This sensor is based on competitive binding between the GA3 and the Rhodamine B (RhB)-labeled GA3 (RhB-GA3) to the MIP film. After the competitive binding, the residual RhB-GA3 on the MIP was electro-oxidized to produce RhB oxide, which could greatly amplify the weak electrochemiluminescence (ECL) signal of luminol. The ECL intensity decreased when the RhB-GA3 was replaced by GA3 molecules in the samples. Accordingly, GA3 was determined in the concentration range from 1 × 10(-11) to 3 × 10(-9) mol/L with a detection limit of 3.45 × 10(-12) mol/L. The sensor shows high sensitivity and selectivity, wide response range, good accuracy, and fast response. Beer samples were assayed by using the sensors, and the recoveries ranging from 96.0% to 103.2% were obtained.