Kaleidoscopic fluorescent arrays for machine-learning-based point-of-care chemical sensing.

Multiplexed analysis allows simultaneous measurements of multiple targets, improving the detection sensitivity and accuracy. However, highly multiplexed analysis has been challenging for point-of-care (POC) sensing, which requires a simple, portable, robust, and affordable detection system. In this work, we developed paper-based POC sensing arrays consisting of kaleidoscopic fluorescent compounds. Using an indolizine structure as a fluorescent core skeleton, named Kaleidolizine (KIz), a library of 75 different fluorescent KIz derivatives were designed and synthesized. These KIz derivatives are simultaneously excited by a single ultraviolet (UV) light source and emit diverse fluorescence colors and intensities. For multiplexed POC sensing system, fluorescent compounds array on cellulose paper was prepared and the pattern of fluorescence changes of KIz on array were specific to target chemicals adsorbed on that paper. Furthermore, we developed a machine-learning algorithm for automated, rapid analysis of color and intensity changes of individual sensing arrays. We showed that the paper sensor arrays could differentiate 35 different volatile organic compounds using a smartphone-based handheld detection system. Powered by the custom-developed machine-learning algorithm, we achieved the detection accuracy of 97% in the VOC detection. The highly multiplexed paper sensor could have favorable applications for monitoring a broad-range of environmental toxins, heavy metals, explosives, pathogens.

Potential-Dependent Electrochemiluminescence for Selective Molecular Sensing of Cyanide.

Although tremendous efforts have been devoted to providing specificity for molecular sensors, most of the methods focus on the structural variation of the binding or reaction site to improve selectivity. Herein, we report a new approach in which a chemical probe, possessing a mediocre recognition site, can successfully discriminate a target among various interferences only with electrochemical manipulation. The synthetic probe (1) was designed to react with a cyanide anion (CN-), and its dicyanovinyl group has selectivity toward CN- along with sulfides and biothiols resulting in similar adducts. However, the binding adduct between 1 and CN- (1-CN-) has significantly different energy levels that are only able to undergo electrochemical oxidation under ∼1.2 V (vs Ag/AgCl), generating strong electrochemiluminescence (ECL). The ECL emission from 1-CN- successfully discriminates CN- without any interferences from other analytes including sulfides and thiols and exhibits a linear correlation with CN- in a range of 1-400 µM (LOD = 0.04 µM, n = 5). Density functional theory (DFT) calculations and electrochemical studies supported the mechanism of CN- discrimination. The approach was finally applied to direct trace analysis of CN- in tap water (≥1 µM) and showed excellent performance suggesting a new, versatile, and rapid determination method for molecular toxins in real samples.

Electrostatic Modification for Promotion of Flavin-Mediated Oxidation of a Probe for Flavin Detection.

Electrostatic effects on the redox photochemistry of synthetic probes (1, 2, and 1-Zn) are examined by adjusting the thermodynamic driving force of their oxidation reactions. The redox photochemistry was simply controlled by introducing a zinc binding site (2,2'-dipicolylamine (DPA)) on the coumarin moiety of probe 2. Zinc complexation produced a positively charged environment on the coumarin (1-Zn), which lowered the electron density of a nearby 9 H-xanthene ring, attenuating the auto-oxidation of 1-Zn by 45 % compared with that of probe 1 at 298 K. The positive net charge of 1-Zn also provided an attractive Coulombic force toward the phosphate of flavin mononucleotide and flavin adenine dinucleotide, which lowered the reduction potential of the electron acceptor (isoalloxazine) and improved intermolecular electron transfer from the 9 H-xanthene ring to isoalloxazine. The flavin-mediated oxidation rate of 1-Zn was increased to 1.5 times that of probe 2. Probe 1-Zn showed highly selective sensing behaviour toward flavins, producing an intense brightness (ϵΦF =2.80×103 m-1  cm-1 ) in the long-wavelength regions (λmax =588 nm) upon flavin-mediated oxidation. Furthermore, probes 1-Zn and 2 were successfully applied to eosinophil imaging and the differential diagnosis of eosinophilia; this demonstrates their use as diagnostic tools.

Single Electron Transfer-Promoted Photochemical Reactions of Secondary N-Trimethylsilylmethyl-N-benzylamines Leading to Aminomethylation of Fullerene C60.

Photoreactions between C60 and secondary N-trimethylsilylmethyl-N-benzylamines were explored to evaluate the feasibility of a new method for secondary aminomethylation of electron acceptors. The results show that photoreactions of C60 with these secondary amines in 10% EtOH-toluene occur to form aminomethyl-1,2-dihydrofullerenes predominantly through a pathway involving single electron transfer (SET)-promoted formation of secondary aminium radicals followed by preferential loss of the α-trimethylsilyl group. The aminomethyl radicals formed in this manner then couple with C60 or C60(•-) to form radical or anion precursors of the aminomethyl-1,2-dihydrofullerenes. In contrast to thermal and photochemical strategies developed previously, the new SET photochemical approach using α-trimethylsilyl-substituted secondary amines is both mild and efficient, and as a result, it should be useful in broadening the library of substituted fullerenes. Moreover, the results should have an impact on the design of SET-promoted C-C bond forming reactions. Specifically, introduction of an α-trimethylsilyl group leads to a change in the chemoselectivity of SET-promoted reactions of secondary amines with acceptors that typically favor aminium radical N-H deprotonation, leading to N-C bond formation. Finally, symmetric and unsymmetric fulleropyrrolidines are also generated in yields that are highly dependent on the electronic properties of arene ring substituents in amines, irradiation time, and solvent.

Homogeneous electrochemical assay for protein kinase activity.

Herein, we report a homogeneous assay for protein kinase activity using an electrochemistry-based probe. The approach involves a peptide substrate conjugated with a redox tag and the phosphate-specific receptor immobilized on an electrode surface. The peptide substrate phosphorylated by a protein kinase binds to the receptor site of the probe, which results in a redox current under voltammetric measurement. Our method was successfully applied even in the presence of citrated human blood and modified to enable a single-use, chip-based electrochemical assay for kinase activity.

Efficient fluorescence "turn-on" sensing of dissolved oxygen by electrochemical switching.

We report on a novel method for sensing oxygen that is based on the use of a perylene diimide dye (1) which is electrochemically reduced to its nonfluorescent dianion form (1(2-)). In the presence of oxygen, the dianion is oxidized to its initial form via an electron-transfer reaction with oxygen upon which fluorescence is recovered. As a result, the fluorescence intensity of the dianion solution increases upon the addition of oxygen gas. Results demonstrate that high sensitivity is obtained, and the emission intensity shows a linear correlation with oxygen content (0.0-4.0% v/v) at ambient barometric pressure. In addition, using electrochemical reduction, oxygen determination becomes regenerative, and no significant degradation is observed over several turnovers. The limit of detection is 0.4% oxygen in argon gas.

Normalizing the Optical Signal Enables Robust Assays with Lateral Flow Biosensors.

Lateral flow assays (LFAs) are widely adopted for fast, on-site molecular diagnostics. Obtaining high-precision assay results, however, remains challenging and often requires a dedicated optical setup to control the imaging environment. Here, we describe quick light normalization exam (qLiNE) that transforms ubiquitous smartphones into a robust LFA reader. qLiNE used a reference card, printed with geometric patterns and color standards, for real-time optical calibration: a photo of an LFA test strip was taken along with the card, and the image was processed using a smartphone app to correct shape distortion, illumination brightness, and color imbalances. This approach yielded consistent optical signal, enabling quantitative molecular analyses under different illumination conditions. We adapted qLiNE to detect cortisol, a known stress hormone, in saliva samples at point-of-use settings. The assay was fast (15 min) and sensitive (detection limit, 0.16 ng/mL). The serial qLiNE assay detected diurnal cycles of cortisol levels as well as stress-induced cortisol increase.

Multielectrode Spectroscopy Enables Rapid and Sensitive Molecular Profiling of Extracellular Vesicles.

Detecting protein markers in extracellular vesicles (EVs) is becoming a useful tool for basic research and clinical diagnoses. Most EV protein assays, however, require lengthy processes-conjugating affinity ligands onto sensing substrates and affixing EVs with additional labels to maximize signal generation. Here, we present an iPEX (impedance profiling of extracellular vesicles) system, an all-electrical strategy toward fast, multiplexed EV profiling. iPEX adopts one-step electropolymerization to rapidly functionalize sensor electrodes with antibodies; it then detects EV proteins in a label-free manner through impedance spectroscopy. The approach streamlines the entire EV assay, from sensor preparation to signal measurements. We achieved (i) fast immobilization of antibodies (<3 min) per electrode; (ii) high sensitivity (500 EVs/mL) without secondary labeling; and (iii) parallel detection (quadruple) in a single chip. A potential clinical utility was demonstrated by directly analyzing plasma samples from glioblastoma multiforme patients.

Electrochemiluminescence in paired signal electrode (ECLipse) enables modular and scalable biosensing.

Electrochemiluminescence (ECL) has an inherently low background and enables precise chemical reactions through electrical control. Here, we report an advanced ECL system, termed ECLipse (ECL in paired signal electrode). We physically separated ECL generation from target detection: These two processes were carried out in isolated chambers and coupled through an electrode. The strategy allowed us to minimize cross-chemical reactions, design electrodes for high ECL signals, and integrate multiple sensors in a chip. As a proof of concept, we implemented an eight-plex ECLipse and applied it to detect host factors in human plasma. ECLipse achieved higher signal-to-noise ratio than conventional ECL assays and was >7000-fold more sensitive than enzyme-linked immunosorbent assay. In a pilot clinical study, we could detect septic conditions by measuring host factors [i.e., interleukin-3 (IL-3), IL-6, and procalcitonin (PCT)]. ECLipse assay further revealed distinct IL-3 and IL-6 patterns in patients with severe acute respiratory syndrome coronavirus 2 infection.

Evaluation of electrogenerated chemiluminescence from a neutral Ir(III) complex for quantitative analysis in flowing streams.

Though recently Ir(III) complexes have attracted much interest in electrochemiluminescent (ECL) analysis due to their high emission in various wavelengths, there were a few studies reported on its analytical applications. In this study, we evaluate the ECL from (pq)(2)Ir(acac) (pq = 2-phenylquinolate, acac = acetylacetonate) for the use in flow injection analysis. An aqueous solution of the analyte and (pq)(2)Ir(acac) passes through the reaction/observation cell, and then ECL reaction is generated by electrochemical initiation on the analyte and (pq)(2)Ir(acac). Tri-n-propylamine (TPrA) is used as a representative analyte for evaluation. Additionally, a comparison is made of the relative ECL intensities obtained for a variety of analytes including oxalate, amino acids, aliphatic amines, and NADH. The (pq)(2)Ir(acac) produces efficient ECL upon TPrA exhibiting the limit of detection of 5 nM with a linear range of 3 orders of magnitude in concentration whereas 20 nM is observed in the conventional Ru(bpy)(3)(2+) system. It shows particular sensitivity advantages for oxalate, proline, and tartaric acid. The ECL generation upon various analytes proposes direct applicability of (pq)(2)Ir(acac) as a post-column detection tool.

Electrogenerated chemiluminescent anion sensing: selective recognition and sensing of pyrophosphate.

Recently, significant advances have been made independently in electrogenerated chemiluminescence (ECL) analysis and supramolecular anion sensing. Herein, we demonstrate a new proof of concept for ECL-based pyrophosphate (PPi) sensing, where the emission intensity is changed by electrochemical turn-on. The ECL PPi sensor (1-2Zn) consists of two orthogonally bonded moieties: boron dipyrromethene (ECL reporter) and a phenoxo-bridged bis(Zn(2+)-dipicolylamine) complex (PPi receptor). The presence of PPi is confirmed from the change in the intensity of green ECL generated from the former when PPi is selectively recognized by the latter. During PPi recognition, changes are caused in the electronic states of the receptor, and this stimulates the attenuation of ECL intensity. The electrochemical "on-off" triggering of light emission upon anion binding forms the basis of a new anion sensing strategy. We expect that green-colored ECL sensing would offer an advantage to current ECL analysis.

Highly sensitive detection of DNA by electrogenerated chemiluminescence amplification using dendritic Ru(bpy)(3)(2+)-doped silica nanoparticles.

This study describes the development and characterization of a novel dendritic signal amplification strategy. It relies on the use of two different Ru(bpy)(3)(2+)-doped silica nanoparticles (Probe(1,2)RSNP and Probe(2c)RSNP) coated with complementary DNAs, which can be simply and conveniently self-assembled to build sandwich-type dendritic architectures on a gold grid. The performance of this dendritic amplification route was demonstrated in conjunction with the electrogenerated chemiluminescent (ECL) detection of the target DNA. Compared to normal amplification, dendritic amplification allowed a 5-fold enhancement of the ECL signals. The higher sensitivity allowed by the dendritic amplification route was attributed to the hybridization between the DNA (Probe(2)DNA) on Probe(1,2)RSNP (normal amplification) and the complementary DNA (Probe(2c) DNA) on the additional Probe(2c)RSNP. As low as 1 fM of 22-bp-long target DNA was clearly detected. The experimental results demonstrated that the ECL intensity achieved through dendritic amplification showed a good linear relationship with the concentration of the target DNA over a wide linear range (10 fM-10 pM).

Data on characterization and electrochemical analysis of zinc oxide and tungsten trioxide as counter electrodes for electrochromic devices.

The data presented in this article are related to a research paper entitled "Implementation of High-Performance Electrochromic Device Based on All-Solution-Fabricated Prussian Blue and Tungsten Trioxide Thin Film"[1]. Zinc oxide nanowire (ZnNW) and tungsten trioxide (WO3) were fabricated by different electrodeposition methods and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and used as counter electrodes. The electrochromic (EC) properties of these devices were characterized using optoelectronic analysis during electrochemical applications.

Advanced method for fabrication of molecularly imprinted mesoporous organosilica with highly sensitive and selective recognition of glyphosate.

In this study, we synthesized molecularly imprinted mesoporous organosilica (MIMO) in the presence of a new precursor having a zwitterionic functional group and an imprint molecule, namely, glyphosate (MIMO-z). The precursor-glyphosate complex engaged in a typical base-catalyzed sol-gel reaction and the introduced zwitterion group remained intact in the framework after the extraction process had been completed. To test the rebinding performance of the target molecule, graphene quantum dots were encapsulated (MIMO-zQ) into pores and the fluorescence intensity change was monitored according to the concentration of glyphosate. When the MIMO-zQ suspension was diluted into the glyphosate solutions, notable fluorescence quenching occurred, right down to sub-nanomolar levels of concentration; 9.2 ± 0.18% quenching at 0.1 nM (0.017 ppb, 17 pg/mL). This result is one of the best reported to date for sensing using MIMO. The synthesized probe also exhibited a distinct signal compared to a series of competing compounds, aminomethylphosphonic acid and glycine; 4.3 ± 0.019% and 3.7 ± 0.041% quenching at 100 nM.

Dynamic Interplay between Transport and Reaction Kinetics of Luminophores on the Operation of AC-Driven Electrochemiluminescence Devices.

Electrochemiluminescence (ECL) involves light emission accompanied by a series of electrochemical processes on luminophores, which has been recently exploited in a new light-emitting device platform, referred to as the ECL device (ECLD). Here, we investigate the influence of the transport of the ECL luminophores and their reaction kinetics on the emission properties of alternating current-voltage-driven ECLDs. A model based on the diffusion and reaction rate equations is developed to predict the operational frequency ( f)-dependent luminance properties of the ECLD. It is found that more frequent generation of the redox precursors with a shorter time interval enhances their probability of encountering each other, and therefore the luminance of the device increases with increasing f initially. The luminance at a higher f, however, is suppressed eventually due to the decreased rate of the electrode reactions. Using the model, the influence of diffusion and reaction rates on the performance of an ECLD is analyzed separately and systematically. The results provide insight on the operation of this emerging class of a light-emitting device platform.

Diffusion controlled multilayer electrocatalysts via graphene oxide nanosheets of varying sizes.

Controlling the architecture of hybrid nanomaterial electrodes is critical for understanding their fundamental electrochemical mechanisms and applying these materials in future energy conversion and storage systems. Herein, we report highly tunable electrocatalytic multilayer electrodes, composed of palladium nanoparticles (Pd NPs) supported by graphene sheets of varying lateral sizes, employing a versatile layer-by-layer (LbL) assembly method. We demonstrate that the electrocatalytic activity is highly tunable through the control of the diffusion and electron pathways within the 3-dimensional multilayer electrodes. A larger-sized-graphene-supported electrode exhibited its maximum performance with a thinner film, due to facile charge transfer by the mass transfer limited in the early stage, while a smaller-sized-graphene-supported electrode exhibited its highest current density with higher mass loading in the thicker films by enabling facile mass transfer through increased diffusion pathways. These findings of the tortuous-path effect on the electrocatalytic electrode supported by varying sized graphene provide new insights and a novel design principle into electrode engineering that will be beneficial for the development of effective electrocatalysts.

Electrochemiluminescent chemodosimeter based on iridium(III) complex for point-of-care detection of homocysteine levels.

Elevated levels of plasma homocysteine (Hcy) are an independent risk factor for cardiovascular disease. Although a routine, rapid, and simple determination of Hcy levels is highly desired, the existing methods are practically limited because of complicated sample preparation and bulky instrumentation. Herein, we report a chemodosimetric approach for one-step analysis of Hcy levels based on the electrochemiluminescence (ECL). A rationally designed cyclometalated iridium(III) complex possessing a phenylisoquinoline main ligand underwent a selective ring-formation reaction with Hcy to generate a binding adduct, which enabled producing highly luminescent excited states, and yielded strong ECL signals on the surface of electrode without any use of enzymes or antibodies. The level of Hcy was successfully monitored by the ECL increment with a linear correlation between 0 and 40µM in 99.9% aqueous media. The approach required neither sample preparation nor bulky instrument, suggesting the point-of-care testing of Hcy levels, and is potentially useful for routine, cost-effective, and precautionary diagnosis of various cardiovascular diseases.

Rhodium Complex and Enzyme Couple Mediated Electrochemical Detection of Adenosine.

Adenosine is one of the nucleoside which plays an important role in signal transduction and neuromodulation. This work proposes a simple electrochemical assay, comprising two enzymes and rhodium complex based electron transfer mediator, for the detection of adenosine. Sequential reaction of adenosine deaminase and L-glutamic dehydrogenase and the supporting cycle between ß-NADH and mediator enable quantitative analysis of adenosine. Role of electron transfer mediator is the conveyance of proton from electrode to ß-NAD(+) for regeneration of ß-NADH. The electrochemical characteristics of electron transfer mediator were also studied. Real-time adenosine detection was carried out using this multiple enzyme based chronoamperometric assay. The analysis results show a low limit of detection (140 µM) and good correspondence between current signal and the adenosine concentration (R (2) = 0.997).

Apparent pH sensitivity of solution-gated graphene transistors.

Solution-gated graphene transistors were developed recently for use in pH sensor applications. The device operation is understood to rely on the capability of hydronium and hydroxide ions in solution to change the electrical properties of graphene. However, hydronium and hydroxide ions are accompanied by other ionic species in a typical acidic or basic solution and, therefore, the roles of these other ionic species must be also considered to fully understand the pH response of such devices. Using series of pH buffer solutions designed carefully, we verified that the magnitude and even the direction of pH-dependent Dirac voltage (VDirac) shift (the typical pH sensing indicator) depend strongly on the concentration and composition of the buffers used. The results indicate that the interpretation of the apparent pH-dependent VDirac response of a solution-gated graphene transistor must include the contributions of the additional ions in the solution.