Dithiothreitol-Lucigenin Chemiluminescent System for Ultrasensitive Dithiothreitol and Superoxide Dismutase Detection.

1,4-Dithiothreitol (DTT), a highly water-soluble and well-known reducing agent for preservation and regeneration of sulfhydryl groups in biomedical applications, has been developed as an efficient and stable coreactant of lucigenin for the first time. DTT efficiently reacts with lucigenin to generate intense chemiluminescence (CL), eliminating the need for external catalysts to facilitate the lucigenin CL. The DTT-lucigenin CL is approximately 15-fold more intense when compared with the lucigenin-H2O2 classical system. Superoxide dismutase (SOD) remarkably quenches the DTT-lucigenin CL. Based on this phenomenon, a newly developed CL approach for the determination of SOD was proposed with a linear range of 0.01-1.5 µg/mL and a limit of detection of 2.2 ng/mL. Various factors affecting the CL emission of the DTT-lucigenin probe were studied and optimized. Plausible mechanistic pathways for the CL coreaction of lucigenin with DTT were proposed and fully discussed. Our proposed method not only has the merit of being selective toward the target analytes but also eliminates the need for the complex synthesis of luminescent probes and facilitates the sensitive detection of SOD in human serum and cosmetics SOD raw material with satisfactory recoveries.

Dimeric G-Quadruplex: An Efficient Probe for Ultrasensitive Fluorescence Detection of Mustard Compounds.

Some mustard compounds (mustards) are highly toxic chemical warfare agents. Some are explored as new anticancer drugs. Therefore, the fast, selective, and sensitive detection of mustards is extremely important for public security and cancer therapy. Mustards mostly target the N7 position on the guanine bases of DNA. The guanine-rich G-quadruplex DNA (G4) has been widely studied in the sensing area, and it was found that dimeric G4 (D-G4) could dramatically light up the fluorescence intensity of thioflavin T (ThT). Based on this, we used for the first time the D-G4 DNA as a selective probe for ultrasensitive fluorescence detection of nitrogen mustard (NM). When NM occupies the N7 on guanine, it can block the formation of the D-G4 structure due to the steric hindrance, and hence, it inhibits the combination of D-G4 with ThT, leading to a sharp decrease of fluorescence intensity. The proposed reaction mechanism is proved using ultraviolet-visible (UV-Vis) spectra, circular dichroism (CD) spectra, and polyacrylamide gel electrophoresis. Herein, the concentration of D-G4/ThT used is as low as 50 nM due to its highly fluorescent performance, enabling both high sensitivity and low cost. NM can be detected with a wide linear range from 10 to 2000 nM. The detection limit of NM reaches a surprisingly low concentration of 6 nM, which is 2 or 3 orders of magnitude lower than that of previously developed fluorescence methods for mustards and simulants.

Rational Design of Electrochemiluminescent Devices.

Electrochemiluminescence (ECL) is a light-emitting process which combines the intriguing merits of both electrochemical and chemiluminescent methods. It is an extensively used method especially in clinical analysis and biological research due to its high sensitivity, wide dynamic range, and good reliability. ECL devices are critical for the development and applications of ECL. Much effort has been expended to improve the sensitivity, portability, affordability, and throughput of new ECL devices, which allow ECL to adapt broad usage scenarios.In this Account, we summarize our efforts on the recent development of ECL devices including new electrodes, ECL devices based on a wireless power transfer (WPT) technique, and novel bipolar electrochemistry. As the essential components in the ECL devices, electrodes play an important role in ECL detection. We have significantly improved the sensitivity of luminol ECL detection of H2O2 by using a stainless steel electrode. By using semiconductor materials (e.g., silicon and BiVO4), we have exploited photoinduced ECL to generate intense emission at much lower potentials upon illumination. For convenience, portability, and disposability, ECL devices based on cheap WPT devices have been designed. A small diode has been employed to rectify alternating current into direct current to dramatically enhance ECL intensity, enabling sensitive ECL detection using a smart phone as a detector. Finally, we have developed several ECL devices based on bipolar electrochemistry in view of the convenience of multiplex ECL sensing using a bipolar electrode (BPE). On the basis of the wireless feature of BPE, we have employed movable BPEs (e.g., BPE swimmers and magnetic rotating BPE) for deep exploration of the motional and ECL properties of dynamic BPE systems. To make full use of the ECL solution, we have dispersed numerous micro-/nano-BPEs in solution to produce intense 3D ECL in the entire solution, instead of 2D ECL in conventional ECL devices. In addition, the interference of ECL noise from driving electrodes was minimized by introducing the stainless steel with a passivation layer as the driving electrode. To eliminate the need for the fabrication of electrode arrays and the interference from the driving electrode and to decrease the applied voltage, we develop a new-type BPE device consisting of a single-electrode electrochemical system (SEES) based on a resistance-induced potential difference. The SEES is fabricated easily by attaching a multiperforated plate to a single film electrode. It enables the simultaneous detection of many samples and analytes using only a single film electrode (e.g., screen-printed electrode) instead of electrode arrays. It is of great potential in clinical analysis especially for multiple-biomarker detection, drug screening, and biological studies. Looking forward, we believe that more ECL devices and related ECL materials and detection methods will be developed for a wide range of applications, such as in vitro diagnosis, point-of-care testing, high-throughput analysis, drug screening, biological study, and mechanism investigation.

Development of luminol-fluorescamine-PVP chemiluminescence system and its application to sensitive tyrosinase determination.

Fluorescamine is a popular fluorescent probe. We report for the first time that luminol chemiluminescence (CL) can be enhanced by fluorescamine in the presence of PVP. The CL intensity of luminol-fluorescamine-PVP is about 26 times stronger than that of luminol. Both the removal of oxygen and the addition of superoxide dismutase (SOD) decrease CL intensity, thiourea and NaN3 have little effect on CL intensities, indicating that O2•- is critical for CL. Interestingly, o-quinone generated from phenol by tyrosinase obviously inhibited the CL intensity. Inspired by such quenching effect on the luminol-fluorescamine-PVP CL system, a sensitive CL sensing for the determination of tyrosinase activity was developed. The method can detect tyrosinase in the range of 0.07-1.5 µg mL-1 (0.19-4.02 U mL-1) with the detection limit of 0.035 µg mL-1 (0.094 U mL-1). Moreover, this method exhibits satisfied recoveries for the spiked human serum samples.

TiO2 Nanomaterials in Photoelectrochemical and Electrochemiluminescent Biosensing.

Titanium dioxide (TiO2) is increasingly being used in biosensing applications. Herein, we review the most recent developments in photoelectrochemical (PEC) and electrochemiluminescent (ECL) biosensing based on TiO2 nanomaterials, as well as the mechanisms that lead to the improved performance of biosensors that incorporate these nanomaterials. The merits of TiO2-based ECL and PEC biosensing strategies are summarized by highlighting some illustrative examples that have been reported within the last 5 years. The future prospects for and challenges in this field are also discussed.

Sonochemiluminescence Based on a Small, Cheap, and Low-Power USB Mesh-Type Piezoelectric Ultrasonic Transducer.

A small, cheap, and low-power mesh-type piezoelectric ultrasonic transducer (MPUT) from a household USB humidifier has been developed as a sonochemiluminescence generator for the first time. The ultrasonication of an MPUT facilitates the generation of reactive oxygen species to trigger sonochemiluminescence. There is no light emission of luminol without sonication. In contrast, the luminescence becomes very intense by ultrasonication using the MPUT and can be readily observed by a smart phone, enabling the visual detection of luminol without adding any coreactants. Interestingly, ascorbic acid, a common chemiluminescence quencher in the literature, increases the sonochemiluminescence in this system. As a result, a sensitive sonochemiluminescence method has been developed for the visual detection of ascorbic acid with a linear range of 1-40 µM and a limit of detection (LOD) of 0.35 µM. Moreover, the visual detection of superoxide dismutase has been achieved on the basis of its quenching effect, which has a linear range of 0.05-2.0 µg/mL and a LOD of 0.018 µg/mL. Because of its advantages of low cost, small size, and low-power consumption, the USB MPUT holds great potential in sonochemiluminescence (SCL) for the development of portable and disposable analysis devices in point-of-care testing and field analysis as well as chemical education.

Improving the limit of detection in portable luminescent assay readers through smart optical design.

Critical biomarkers of disease are increasingly being detected by point-of-care assays. Chemiluminescence (CL) and electrochemiluminescence (ECL) are often used in such assays due to their convenience and that they do not require light sources or other components that could complicate or add cost to the system. Reports of these assays often include readers built on a cellphone platform or constructed from low-cost components. However, the impact the optical design has on the limit of detection (LOD) in these systems remains unexamined. Here, we report a theoretical rubric to evaluate different optical designs in terms of maximizing the use of photons emitted from a CL or ECL assay to improve the LOD. We demonstrate that the majority of cellphone designs reported in the literature are not optimized, in part due to misunderstandings of the optical tradeoffs in collection systems, and in part due to limitations imposed on the designs arising from the use of a mobile phone with a very small lens aperture. Based on the theoretical rubric, we design a new portable reader built using off-the-shelf condenser optics, and demonstrate a nearly 10× performance enhancement compared to prior reports on an ECL assays running on a portable chip.

3D Printed Rotating Acentric Binary-Disk Electrode.

Rotating ring-disk electrode (RRDE) is a generator-collector electrochemical system widely used as an electroanalytical and kinetic device. However, RRDEs are costly and difficult to fabricate, particularly when the electrode material is fragile, small, and scarce. Taking advantage of readily available 3D printing technology an alternative generator-collector system was developed: rotating acentric binary-disk electrode (RABDE). RABDE consists of two close acentric disk electrodes arranged in a cylindrical matrix so that the line connecting their centers is perpendicular to radius of the device passing through the center of generator electrode. In contrast to RRDE that is based on radial flow velocity for mass transfer between the generator and the collector, RABDE mostly takes advantage of the larger tangential flow velocity. RABDE thus exhibits higher current densities than RRDE for a same rotation rate and evidences much better electroanalytical performances. These increased performances were tested and quantified using typical analytes: potassium ferricyanide system, copper ion system, and oxygen reduction reaction in alkaline solution.

Determination of Concentrated Hydrogen Peroxide Free from Oxygen Interference at Stainless Steel Electrode.

H2O2 is frequently used at high concentrations in various applications. It is very challenging to detect high concentrations of H2O2 and to eliminate oxygen interference for H2O2 detection through electrochemical reduction. In the present investigation, the electrochemistry of H2O2 at stainless steel electrode has been carried out for the first time. A cathodic peak for H2O2 reduction was observed at about -0.40 V, and no cathodic peak for dissolved oxygen reduction was observed on type 304 stainless steel electrode. Amperometric determination of H2O2 on type 304 stainless steel electrode displayed a linear range from 0.05 up to 733 mM with a detection limit of 0.02 mM (S/N = 3) and a sensitivity of 16.7 µA mM-1 cm-2. The type 304 stainless steel electrode not only shows much higher upper limit than other reported electrodes for the detection of concentrated H2O2 but also is free from oxygen interference, which is of great importance for practical applications. This method could detect H2O2 in wound wash and lake water with excellent recoveries. Moreover, we successfully applied the stainless steel electrode to determine glucose using glucose oxidase to catalyze the oxidation of glucose to generate hydrogen peroxide. The linear range for glucose is between 0.5 and 25 mM, which covers clinically important blood glucose concentrations well.

A single-electrode electrochemical system for multiplex electrochemiluminescence analysis based on a resistance induced potential difference.

Developing low-cost and simple electrochemical systems is becoming increasingly important but still challenged for multiplex experiments. Here we report a single-electrode electrochemical system (SEES) using only one electrode not only for a single experiment but also for multiplex experiments based on a resistance induced potential difference. SEESs for a single experiment and multiplex experiments are fabricated by attaching a self-adhesive label with a hole and multiple holes onto an ITO electrode, respectively. This enables multiplex electrochemiluminescence analysis with high sensitivity at a very low safe voltage using a smartphone as a detector. For the multiplex analysis, the SEES using a single electrode is much simpler, cheaper and more user-friendly than conventional electrochemical systems and bipolar electrochemical systems using electrode arrays. Moreover, SEESs are free from the electrochemiluminescent background problem from driving electrodes in bipolar electrochemical systems. Since numerous electrodes and cover materials can be used to fabricate SEESs readily and electrochemistry is being extensively used, SEESs are very promising for broad applications, such as drug screening and high throughput analysis.

Amplified electrochemical hydrogen peroxide reduction based on hemin/G-quadruplex DNAzyme as electrocatalyst at gold particles modified heated copper disk electrode.

A new gold particles modified heated copper disk electrode (Au-HCuDE) with direct current was fabricated. The hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) was self-assembled on the heated electrode and resulted in a new biosensor denoted as HRP-DNAzyme/Au-HCuDE. By controlling the temperature of the surface of the electrode, the dramatic temperature effect on the electrocatalytic reduction of H2O2 at HRP-DNAzyme/Au-HCuDE sensing platform was demonstrated. This electrocatalytic activity of HRP-DNAzyme was enhanced with electrode temperature elevated. This method was thus preliminarily used to develop an electrochemical biosensor for highly sensitive detection of H2O2. A detection limit of 1.6×10(-7) M could be obtained (S/N=3) with an electrode temperature of 50 °C, which was more than one magnitude lower than that at electrode temperature of 0 °C. This heated electrochemical biosensor shows many merits such as easy fabrication and simple heating equipment, low cost, high thermal stability, and high sensitivity and good reproducibility.