Ultrasensitive Glutathione-Mediated Facile Split-Type Electrochemiluminescence Nanoswitch Sensing Platform

Etching of Ag nanoparticles triggered bidirectional regulation for electrochemiluminescence ratiometric immunoassay

A highly efficient ratiometric electrochemiluminescence (ECL) immunoassay was explored by bidirectionally regulating the ECL intensity of two luminophors. The immunoassay was conducted in a split-type mode consisting of an ECL detection procedure and a sandwich immunoreaction. The ECL detection was executed using a dual-disk glassy carbon electrode modified with two potential-resolved luminophors (g-C3N4-Ag and Ru-MOF-Ag nanocomposites), and the sandwich immunoreaction using glucose oxidase (GOx)-modified SiO2 nanospheres as labels was carried out in a 96-well plate. The Ag nanoparticles (NPs) acted as bifunctional units both for triggering the resonance energy transfer (RET) with g-C3N4 and for accelerating the electron transfer rate of the Ru-MOF-Ag ECL reaction. When the H2O2 catalyzed by GOx in the 96-well plate was transferred to the dual-disk glass carbon electrode, the doped Ag NPs in the two luminophors could be etched, thus destroying the RET between C3N4 and the accelerated reaction to Ru-MOF, resulting in an opposite trend in the ECL signal outputted from the dual disks. Using the ratio of the two signals for quantification, the constructed immunosensor for a model target, i.e. myoglobin, exhibited a low detection limit of 4.7 × 10-14 g/mL. The ingenious combination of ECL ratiometry, bifunctional Ag NPs, and a split-type strategy effectively reduces environmental and human errors, offering a more precise and sensitive analysis for complex samples.

Nanoreactor based on Cu nanoparticles confined in B, N co-doped porous carbon nanotubes for glutathione biosensing

A cost-effective approach has been developed to synthesize Cu nanoparticles encapsulated into B and N double-doped carbon nanotubes (Cu@BCNNTs) by one-step pyrolysis. According to the specific binding of Cu-Cl and Cu-glutathione (GSH), we employed Cu@BCNNTs to build an electrochemical sensing platform to detect GSH. The unique space-confined structure can prevent Cu nanoparticles from agglomeration. In addition, B and N co-doped porous hollow tubes can improve the electrochemical conductivity, expand the number of active sites, enhance surface adsorption, and shorten the transport path. These favorable characteristics of Cu@BCNNTs make them have excellent electrocatalytic properties. These results display that the prepared sensor can detect GSH from 0.5 to 120 μM with a detection limit of 0.024 μM. The obtained sensors can be successfully applied in the human serum with recovery of GSH ranging from 100.2 to 103.9%. This work provides a new vision to synthesize nanoparticles confined in a hollow tube for the applications in biosensing and medical diagnostics.

A smartphone-assisted colorimetric and photothermal probe for glutathione detection based on enhanced oxidase-mimic CoFeCe three-atom nanozyme in food

The rational fabrication of point-of-care testing (POCT) featuring simplicity, rapidity, low cost, portability, high sensitivity and accuracy is crucial for maintaining food safety in resource-limited locations and home healthcare but remains challenging. Herein, we report a universal colorimetric-photothermal-smartphone triple-mode sensing platform for POC food-grade glutathione (GSH) detection. This simple sensing platform for GSH detection takes merits of three techniques: commercially available filter paper, thermometer and smartphone via an excellent CoFeCe-mediated oxidase-like activity. This strategy allows CoFeCe three-atom hydroxide to efficiently convert dissolved oxygen into O₂^·- and catalyzes 3, 3', 5, 5'-tertamethylbenzidine (TMB) to generate an oxidized TMB with remarkable color changes and photothermal effect, resulting in a colorimetric-temperature-color triple-mode signal output. The constructed sensor exhibits high sensitivity with a limit of detection of 0.092 μM for GSH detection. We expect this sensing platform can be easily modified for the determination of GSH in commercial samples with the simple testing strips.

Zn2+-Induced Gold Cluster Aggregation Enhanced Electrochemiluminescence for Ultrasensitive Detection of MicroRNA-21

Herein, Zn²⁺-induced gold cluster aggregation (Zn²⁺-GCA) as a high-efficiency electrochemiluminescence (ECL) emitter is first employed to construct an ECL biosensor to ultrasensitively detect microRNA-21 (miRNA-21). Impressively, Zn²⁺ not only can induce the aggregation of monodispersed gold clusters (Au NCs) to limit the ligand vibration of Au NCs for improving ECL emission but also can be utilized as a coreaction accelerator to catalyze the dissociation of coreactant S₂O₈^2- into sulfate radicals (SO₄^•-) to improve the interaction efficiency between Zn²⁺-GCA and S₂O₈^2-, resulting in further intense ECL emission. Compared to Au NCs stabilized by bovine serum albumin with ECL efficiency of 0.40%, Zn²⁺-GCA possessed high ECL efficiency of 10.54%, regarding the [Ru(bpy)₃]²⁺/S₂O₈^2- system as a standard. Furthermore, output DNA modified with poly adenine (polyA) obtained from enzyme-free target recycling amplification can be efficiently immobilized on the surface of gold nanoparticles (Au NPs) to reduce the defect of special design, cumbersome operation, and low stability. Thus, an ultrasensitive ECL biosensor based on the Zn²⁺-GCA/S₂O₈^2- ECL system and enzyme-free target recycling amplification achieved ultrasensitive detection of miRNA-21 with the detection limit of 44.7 aM. This strategy presents a new idea to design highly efficient ECL emitters, which is expected to be used in the field of bioanalysis for clinical diagnosis.

PB@PDA nanocomposites as nanolabels and signal reporters for separate-type cathodic photoelectrochemical immunosensors in the detection of carcinoembryonic antigens

Photoelectrochemical (PEC) immunoassays exhibiting high sensitivity and decent operability have considerable potential in areas such as cancer diagnostics. In particular, cathodic PEC configurations can prevent interference from reductive substances, which can occur in biological samples; however, challenges remain in terms of sensitivity and operability. In this study, separate-type PEC immunoassays were developed for carcinoembryonic antigen (CEA) by combining microplate-based immune recognition and off-on cathodic PEC detection. Polydopamine (PDA)-coated Prussian blue (PB) nanoparticles (PB@PDA NPs) were used as signal tags to label the detection antibody. The PB NPs and PDA captured on the microplates both disassembled under strongly alkaline conditions to generate redox-active electron acceptors. The disassembled products were quantitatively transferred to PEC detection cells and synergistically enhanced the PEC current with microstructured BiOI, which operated as a cathodic semiconductor electrode. As proof of principle, carcinoembryonic antigen (CEA) was applied to elucidate the potential application of PEC immunoassay in clinical diagnosis, and the obtained linear range of the sensor was 0.001-100 ng mL^-1 with the detection limit of 54.9 fg mL^-1 (S/N = 3). The proposed separate-type off-on PEC strategy showed high sensitivity and decent operability for CEA detection, indicating its potential for the identification of other tumor markers.

Heterojunction MnO2-nanosheet-decorated Ag nanowires with enhanced oxidase-like activity for the sensitive dual-mode detection of glutathione

The biocatalytic design of nanomaterials with enzyme-like activity is considered a reliable and promising toolkit for the generation of diagnostic agents in complex biological microenvironments. However, the preparation of nanomaterials while maintaining a high catalytic activity in tumor cells (pH 6.0-6.5) poses a prominent challenge. Herein, we constructed a biomimetic enzyme-trigged dual-mode system with colorimetry at 652 nm and photothermal biosensors to detect glutathione based on hollow MnO₂-nanosheet-decorated Ag nanowires (Ag@MnO₂) as an oxidase-like nanozyme. As expected, Ag@MnO₂ catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the absence of H₂O₂, leading to a blue-colored oxidized TMB (oxTMB) that displayed oxidase-like activity in pH 6.0. Interestingly, the portable dual-mode colorimetry and photothermal method for GSH was developed based on the redox reaction between GSH and oxTMB. This detection method exhibited a wide linear range of 0.1-55 μM for GSH with a low detection limit of 0.08 μM. This work highlights a new insight into nanotechnology by taking advantage of biomimetic design in biological analysis.

The Mn-modified porphyrin metal-organic framework with enhanced oxidase-like activity for sensitively colorimetric detection of glutathione

The selective detection of glutathione (GSH) has been used as important colorimetric probe for human health. Herein, we used a facile method to synthesize manganese ions modified porphyrin metal-organic framework (PCN-224-Mn) with a size of 125.7 ± 14.2 nm and zeta potential of -3.9 ± 0.5 mV. We showed that PCN-224-Mn catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the absence of H₂O₂, resulting in a blue-colored oxidized TMB (oxTMB) that exhibits oxidase-like activity. Furthermore, a simple colorimetric detection method for GSH was developed based on the oxidase-like activity of PCN-224-Mn. This method shows wide linear detection range of 0.5-60 μM for GSH with a much lower detection limit of 0.233 μM. Finally, the recovery of colorimetric sensor of PCN-224-Mn suggests its great potential as a biosensor. As the catalytically active site, the manganese porphyrin unit plays a major role in the oxidase-like property and detection ability of PCN-224-Mn. Our data suggest that GSH detection method using PCN-224-Mn has great potential in multiple applications in the future.

Antifouling Electrochemical Biosensor Based on Conductive Hydrogel of DNA Scaffold for Ultrasensitive Detection of ATP

As an energy supplier, ATP plays an important role in various life activities, and there is an urgent need to develop an effective means of detecting ATP. However, the traditional sensors face serious nonspecific adsorption. In this work, an antifouling electrochemical biosensor based on the interpenetrating network of Y-DNA scaffold and polyaniline hydrogel was designed for ATP detection. The polyaniline hydrogel was conducive to the transport of electrons and ions, the structure of Y-DNA cross-linked by ATP aptamers in the polyaniline hydrogel achieved the effect of signal amplification. Super hydrophilic cellulose nanocrystals (CNCs) and zwitterion polypeptide sequence (Pep) were doped to play a synergistic antifouling effect. The hydrogel sensor we have built has a wide linear range of 0.1 pM-1 μM for ATP detection and a low detection limit of 0.025 pM (S/N = 3). For ATP detection in actual serum samples, the recovery of this sensor was 99.5%-106%, and the relative standard deviation was 0.4%-2.88%. It is proven that the sensor has good ATP detection performance, and it will provide a certain reference value for the detection of other biological small molecules.

Versatile Electrochemical Biosensor Based on the Target-Controlled Capture and Release of DNA Nanotubes for the Ultrasensitive Detection of Multiplexed Biomarkers

Herein, an ultrasensitive and versatile electrochemical biosensor was developed through the target-controlled capture and release of signal probe-loaded DNA nanotube for the ultrasensitive detection of two different types of cancer-related biomarkers, microRNA-21 (miRNA-21) and glutathione (GSH). In this system, target 1 (miRNA-21) first triggered duplex-specific nuclease (DSN)-assisted recycle amplification to generate numerous disulfide-linked DNA strands (DL), which could effectively capture DNA nanotube to immobilize methylene blue (MB) to produce remarkable electrochemical signals and achieve the ultrasensitive detection of miRNA-21 with a detection limit down to 32.6 aM. Furthermore, in the presence of target 2 (GSH), the electrochemical signal was significantly reduced by a thiol-disulfide bond exchange reaction on DL to release MB-immobilized DNA nanotubes away from the sensing interface, which enabled the sensitive analysis of GSH with a detection limit of 0.379 nM. Impressively, this strategy could achieve ultrasensitive detection of different types of biomarkers to prominently lessen false-positive responses from the current sensing methods toward a single biomarker or the same type of biomarker and remarkably heighten the accuracy and precision of early cancer diagnosis. Meanwhile, the proposed electrochemical biosensor made it possible to realize the regenerative analysis of targets over four times without extra fuel, which could conspicuously improve the analytical efficiency compared with that of traditional biosensing assays. As a result, this study might open up novel insights to design a versatile and multifunctional sensing platform and encourage deeper exploration for detecting different types of biomarkers in the fields of early disease diagnosis and biochemical research.

Point-of-care biochemical assays using electrochemical technologies: approaches, applications, and opportunities

Against the backdrop of hidden symptoms of diseases and limited medical resources of their investigation, in vitro diagnosis has become a popular mode of real-time healthcare monitoring. Electrochemical biosensors have considerable potential for use in wearable products since they can consistently monitor the physiological information of the patient. This review classifies and briefly compares commonly available electrochemical biosensors and the techniques of detection used. Following this, the authors focus on recent studies and applications of various types of sensors based on a variety of methods to detect common compounds and cancer biomarkers in humans. The primary gaps in research are discussed and strategies for improvement are proposed along the dimensions of hardware and software. The work here provides new guidelines for advanced research on and a wider scope of applications of electrochemical biosensors to in vitro diagnosis.

A near-infrared light-driven photoelectrochemical aptasensing platform for adenosine triphosphate detection based on Yb-doped Bi2S3 nanorods

Due to its capability of low spectral interference, high light stability, and minimal photodamage to biological species, near-infrared (NIR) light is advantageous in biosensing and biochemical analysis. This work developed a photoelectrochemical (PEC) aptasensor for adenosine triphosphate (ATP) detection using NIR light as the irradiation source. In order to utilize NIR light, we prepared Yb-doped Bi₂S₃ (Yb-Bi₂S₃) nanorods to act as photoelectric transducing materials. Due to the unfilled 4f orbitals of Yb which introduced the impurity level between the valence band and conduction band of Bi₂S₃, Yb-Bi₂S₃ exhibited admirable photo-to-current conversion efficiency under NIR light irradiation. The Yb-Bi₂S₃ modified electrode was employed to construct a NIR light-driven PEC sensor using an ATP-binding aptamer as the recognition element. When ATP was present, the photocurrent signal of the proposed aptasensor declined, owing to the formation of an ATP-aptamer complex which enhanced the steric hindrance of electron transfer on the electrode. Under optimal conditions, the sensor showed a sensitive response to ATP in the concentration range from 0.5 to 300 nmol L^-1 with a detection limit of 0.1 nmol L^-1. The proposed aptasensor exhibited high selectivity, good repeatability and desirable stability. Moreover, it was successfully applied to ATP detection in human serum samples.

Self-assembled nanoplatforms with ZIF-8 as a framework for FRET-based glutathione sensing in biological samples

A nanoprobe was constructed by embedding QDs and a rhodamine B derivative (RBD) into ZIF-8. Then, the ultraviolet absorption of RBD that reacted with glutathione can overlap with the emission spectrum of the QDs, causing FRET-based glutathione sensing.