Hierarchical hematite/TiO2 nanorod arrays coupled with responsive mesoporous silica nanomaterial for highly sensitive photoelectrochemical sensing

A Paper-Based Photoelectrochemical Sensing Platform Based on In Situ Grown ZnO/ZnIn2S4 Heterojunctions onto Paper Fibers for Sensitively Detecting AFP

Nowadays, developing a cost-effective, easy-to-operate, and efficient signal amplification platform is of important to microfluidic paper-based analytical devices (μPAD) for end-use markets of point-of-care (POC) assay applications. Herein, an ultrasensitive, paper-based photoelectrochemical (PEC) bioassay platform is constructed by in situ grown ZnO/ZnIn₂S₄ heterojunctions onto paper fibers, which acted as photoactive signal amplification probes for enhancing the sensitivity of antibodies-based diagnostic assays, for the sensitive detection of alpha-fetoprotein (AFP) targets. The crystalline flake-like ZnIn₂S₄ composited with hexagonal nanorods (NRs) morphology of ZnO is an in situ grown, at the first time, onto cellulose fibers surface supported with Au nanoparticle (Au NP) modification to improve conductivity of the device working zone. The obtained composites on paper fibers are implemented as a flexible paper-based photoelectrode to realize remarkable performance of the fabricated μPAD, resulting from the enhanced PEC activity of heterojunctions with effective electron-hole pair separation for accelerating photoelectric conversion efficiency of the sensing process under light irradiation. Once the target AFP was introduced into the biosensing interface assistant, with a specific recognition interaction of AFP antibody, a drastically photocurrent response was generated, in view of the apparent steric effects. With the concentration increase of AFP targets, more immune conjugates could be confined onto the biosensing interface, eventually leading to the quantitative decrease of photocurrent intensity. Combined with an ingenious origami design and permitting the hydrophobic/hydrophilic conversion procedure in the bioassay process, the ultrasensitive PEC detection of AFP targets was realized. Under the optimized conditions, the level of AFP could be sensitively tracked by the prepared μPAD with a liner range from 0.1 to 100 ng mL^-1 and limit of detection of 0.03 ng mL^-1. This work provides a great potential application for highly selective and sensitive POC testing of AFP, and finally, developments for clinical disease diagnosis.

Photoelectrochemical sandwich immunoassay of brain glycogen phosphorylase based on methyl orange-sensitized TiO2 nanorods

The photoelectrochemical immunoassay of glycogen phosphorylase BB (GPBB) was studied. A methyl orange/TiO₂ nanorod heterojunction was constructed on a fluorine-doped tin oxide electrode by hydrothermal synthesis, calcination, and chemical adsorption. A sandwich immune structure consisting of GPBB as the first antibody, GPBB, and a CdS@mesoporous silica-ascorbic acid (AA)-GPBB as secondary antibody composite was constructed on each of the selected well surfaces of a 96-well microplate. By adding mercaptoethylamine to structurally destroy the secondary antibody composite and release the electron donor AA, the amplification of photocurrent, and thus the "off-on" photoelectrochemical biosensing of GPBB were realized. The use of the 96-well microplate provides good reproducibility of the assembled immune structures and eliminates the possible effect of the photogenerated hole-induced protein oxidation on the photocurrent. The relevant electrodes and materials were characterized by electrochemistry, UV-vis diffuse reflectance spectra, Fourier transform infrared spectroscopy, X-ray diffractometer, scanning electron microscopy/energy dispersive spectroscopy, transmission electron microscopy and BET method. Under the optimal conditions, the photocurrent was linear with the logarithm of GPBB concentration from 0.005 to 200 ng mL^-1 and with a limit of detection of 1.7 pg mL^-1 (S/N = 3). Satisfactory results were obtained in the analysis of real serum samples. A sandwich immune structure consisting of GPBB first antibody, GPBB, and a CdS@mesoporous silica-ascorbic acid (AA)-GPBB secondary antibody composite was constructed on each of the selected well surfaces of a 96-well microplate. By adding mercaptoethylamine to structurally destroy the secondary antibody composite and release the electron donor AA, the amplification of photocurrent, and thus the "off-on" photoelectrochemical biosensing of GPBB were realized.

Photoelectrochemical Detection of Exosomal miRNAs by Combining Target-Programmed Controllable Signal Quenching Engineering

MicroRNAs extracted from exosomes (exosomal miRNAs) have recently emerged as promising biomarkers for early prognosis and diagnosis. Thus, the development of an effective approach for exosomal miRNA monitoring has triggered extensive attention. Herein, a sensitive photoelectrochemical (PEC) biosensing platform is demonstrated for exosomal miRNA assay via the target miRNA-powered λ-exonuclease for the amplification strategy. The metal-organic framework (MOF)-decorated WO₃ nanoflakes heterostructure is constructed and implemented as the photoelectrode. Also, a target exosomal miRNA-activatable programmed release nanocarrier was fabricated, which is responsible for signal control. Hemin that acted as the electron acceptor was prior entrapped into the programmed control release nanocarriers. Once the target exosomal miRNAs-21 was introduced, the as-prepared programmed release nanocarriers were initiated to trigger the release of hemin, which enabled the quenching of the photocurrent. Under the optimized conditions, the level of exosomal miRNAs-21 could be accurately tracked ranging from 1 fM to 0.1 μM with a low detection limit of 0.5 fM. The discoveries illustrate the possibility for the rapid and efficient diagnosis and prognosis prediction of diseases based on the detection of exosomal miRNAs-21 and would provide feasible approaches for the fabrication of an efficient platform for clinical applications.

Electrochemiluminescence biosensor for microRNA determination based on AgNCs@MoS2 composite with (AuNPs-Semicarbazide)@Cu-MOF as coreaction accelerator

A novel electrochemiluminescence (ECL) biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide (AgNCs@MoS₂) as an ECL material, peroxodisulfate (S₂O₈^2-) as a co-reactant, and semicarbazide (Sem) as a co-reaction accelerator. Firstly, hairpin probe H_a modified on AgNCs@MoS₂/GCE was unfolded based on its hybridization with target microRNA. Then, the unfolded H_a can further be hybridized with another hairpin DNA of H_b on (AuNPs-semicarbazide)@Cu-MOF, resulting in the release of target microRNA, which further causes a cyclic hybridization. This creates more (AuNPs-semicarbazide)@Cu-MOF on the electrode surface, achieving cyclic hybridization signal amplification. Strikingly, due to the presence of Sem, accelerating the reduction of S₂O₈^2- and resulting in the generation of more oxidant intermediates of SO₄^2-, the amount of excited states of Agincreases to further amplify the ECL signal. The biosensor exhibited high sensitivity with a low LOD of 1.067 fM, indicating that the introduction of co-reaction accelerators can provide an effective method for signal amplification. The applicability of this method was assessed by investigating the effect of Pb(II) ion on miRNA-162a expression level in maize seedling leaves. A novel electrochemiluminescence biosensor was fabricated for miRNA-162a detection by using silver nanoclusters/molybdenum disulfide as an ECL material, peroxodisulfate as a co-reactant, and semicarbazide as a co-reaction accelerator.

Preparation of pH-sensitive chitosan/polyvinylpyrrolidone/α-Fe2O3 nanocomposite for drug delivery application: Emphasis on ameliorating restrictions

Chitosan (CS)/polyvinylpyrrolidone (PVP)/hematite (α-Fe₂O₃) nanocomposites loaded with Doxorubicin (drug model) were synthesized via an oil-in-water emulsification method to develop a biocompatible and pH-sensitive drug nanocarrier for the first time. A hydrogel, including CS, PVP, and α-Fe₂O₃, was fabricated successfully with glutaraldehyde (GA) as the cross-linker. Incorporating α-Fe₂O₃ into CS/PVP hydrogel improved the pH-sensitivity and developed beneficial hydrogel. FTIR and XRD analysis illustrated physical interactions between polymer-polymer, polymer-drug, and crystalline behavior of prepared nanocomposite. These analyses also confirmed chemical bonding in nanocomposite's structure. The FE-SEM analysis showed successful impregnation of α-Fe₂O₃ into CS/PVP matrix and spherical structure. To clarify the size distribution and surface charge of the drug-loaded nanocomposite (CS/PVP/α-Fe₂O₃/Dox), DLS and zeta analyses were conducted. They showed the mean size of nanocomposites at about 247 nm. Drug-loaded CS/PVP/α-Fe₂O₃ nanocomposite and CS/PVP/Dox were studied for their release behavior and kinetics. Furthermore, the effect of α-Fe₂O₃ on release from CS/PVP/α-Fe₂O₃/Dox nanocomposite was investigated. That showed an increase in encapsulation of Doxorubicin and beneficial release behavior such as slow-release and retention effect. The release from this drug-loaded nanocomposite revealed excellent pH-sensitive and controlled release of the drug. Besides, the in vitro cytotoxicity and cell apoptosis were studied to recognize biological properties. These analyses revealed that drug-loaded nanocomposite caused high inhibition to MCF-7 cells in presence of α-Fe₂O₃ and proved the hematite's anti-cancer effect. By and large, this study confirmed CS/PVP/α-Fe₂O₃ nanocomposites as a potential candidate for the controlled pH-sensitive release of the drug.

MoS2-ReS2 Heterojunctions from a Bimetallic Co-chamber Feeding Atomic Layer Deposition for Ultrasensitive MiRNA-21 Detection

Rhenium disulfide (ReS₂), which possessed a unique direct band gap from the bulk to monolayer, played a very important role in establishing optoelectronic devices, while the rapid recombination of electron-hole pairs might hinder its further applications. Therefore, to improve its photocurrent performance, a bimetallic co-chamber feeding atomic layer deposition (ALD) with a precise dose regulation strategy was used to fabricate MoS₂-ReS₂ heterojunctions with a controllable Mo-to-Re ratio in this work. Furthermore, because of the controlled addition of Mo atoms, the electron-transfer capacity, carrier mobility, and photocurrent response of these heterojunctions were significantly improved among which the sample obtained under 100 supercycles (one supercycle for this sample consists of the following in turn: one ReCl₅ pulse, one H₂S pulse, one ReCl₅ pulse, one MoCl₅ pulse, and one H₂S pulse; the real Mo-to-Re ratio R_r = 57.9%) exhibited the best photocurrent response. Due to the significant improvement in optoelectronic performance, a photoelectrochemical (PEC) biosensor with the basis of the above optimized sample could achieve the ultrasensitive detection of cancer-related miRNA-21 ranging from 10 aM to 1 nM with a low detection limit of 2.8 aM.

Novel Electron Donor Encapsulation Assay Based on the Split-type Photoelectrochemical Interface

In this research, a controlled-release photoelectrochemical (PEC) immunosensor is proposed on the basis of a novel encapsulation strategy by all-inorganic semiconductor materials. The controlled-release transmit system has been prepared and represented on account of a group-functional mesoporous silica nanosphere (MSN), utilizing surface-functionalized cadmium sulfide (CdS) nanoparticles as mobilizable caps to encapsulate a PEC electron donor ascorbic acid (AA) within the MSN mesoporous structure. This encapsulation strategy proceeds without any enzyme and acid/alkali to achieve the release of an electron donor. The complex is formed by encapsulating AA within MSN with CdS (CdS@MSN-AA) as a signal amplifier labeled on the secondary antibody. In addition, the immunological recognition process was performed in a 96-well plate, and the reciprocal interference between biorecognition and PEC analysis could be eliminated through a split-type framework. Bi₂S₃-sensitized porous In₂O₃ nanoparticles as a substrate matrix provide basic PEC response. The developed sensor exhibited a mensurable output of procalcitonin (PCT) concentration (as an example) in the detection range of 0.001-200 ng/mL along with a limit of detection of 0.31 pg/mL. Featuring the novel method for electron release, this sensitive PEC strategy provides an innovative way for the potential application for other targets.

Wide-Spectrum-Responsive Paper-Supported Photoelectrochemical Sensing Platform Based on Black Phosphorus-Sensitized TiO2

A wide-spectrum-responsive paper-based photoelectrochemical (PEC) sensor based on black phosphorus (BP) quantum dots (QDs)-sensitized titanium dioxide (TiO₂-BP QDs) for prostate-specific antigen (PSA) detection was presented herein. Carbon nanotubes (CNTs) were first coated on paper to form a flexible conductive paper electrode. TiO₂ nanoparticles were then in situ synthesized on the CNTs-modified paper working electrode with direct liquid-phase hydrolysis with normal temperature, shirtsleeve operation, and gentle solution. Meanwhile, BP QDs, derived from two-dimensional BP nanosheets, can harvest light from the ultraviolet to near-infrared region, broaden efficient utilization of light, add a new dimension to BP research, and impel the high expectation on the potentials of QDs. To implement an assay protocol, exciton-plasmon interactions between TiO₂-BP QDs and gold nanoparticles were introduced into the PEC sensing platform for high sensitivity detection of the PSA antigen. Under the optimal conditions, this proposed method exhibited a linear response ranging from 0.005 to 50 ng/mL with a detection limit of 1 pg/mL. This sensing protocol offered a promising analytical method with favorable properties of high selectivity, stability, and reproducibility.

Ultrasensitive photoelectrochemical biosensor for MiRNA-21 assay based on target-catalyzed hairpin assembly coupled with distance-controllable multiple signal amplification

Here, with the target-catalyzed hairpin assembly generated dsDNA (HP1-HP2) to synchronously control the departure of quencher ferrocene and approach of sensitizer methylene blue, a distance-controllable multiple signal amplification based photoelectrochemical biosensor was proposed for MiRNA-21 assay.

Avenues Toward microRNA Detection In Vitro: A Review of Technical Advances and Challenges

Over the decades, the biological role of microRNAs (miRNAs) in the post-transcriptional regulation of gene expression has been discovered in many cancer types, thus initiating the tremendous expectation of their application as biomarkers in the diagnosis, prognosis, and treatment of cancer. Hence, the development of efficient miRNA detection methods in vitro is in high demand. Extensive efforts have been made based on the intrinsic properties of miRNAs, such as low expression levels, high sequence homology, and short length, to develop novel in vitro miRNA detection methods with high accuracy, low cost, practicality, and multiplexity at point-of-care settings. In this review, we mainly summarized the newly developed in vitro miRNA detection methods classified by three key elements, including biological recognition elements, additional micro-/nano-materials and signal transduction/readout elements, their current challenges and further applications are also discussed.

Research advances in the detection of miRNA

MicroRNAs (miRNAs) are a family of endogenous, small (approximately 22 nucleotides in length), noncoding, functional RNAs. With the development of molecular biology, the research of miRNA biological function has attracted significant interest, as abnormal miRNA expression is identified to contribute to serious human diseases such as cancers. Traditional methods for miRNA detection do not meet current demands. In particular, nanomaterial-based methods, nucleic acid amplification-based methods such as rolling circle amplification (RCA), loop-mediated isothermal amplification (LAMP), strand-displacement amplification (SDA) and some enzyme-free amplifications have been employed widely for the highly sensitive detection of miRNA. MiRNA functional research and clinical diagnostics have been accelerated by these new techniques. Herein, we summarize and discuss the recent progress in the development of miRNA detection methods and new applications. This review will provide guidelines for the development of follow-up miRNA detection methods with high sensitivity and specificity, and applicability to disease diagnosis and therapy.

Paper-Supported Self-Powered System Based on a Glucose/O2 Biofuel Cell for Visual MicroRNA-21 Sensing

The exploitation of self-powered devices that get rid of the power source restriction represents the development tendency of sensing systems. Herein, a paper-supported glucose/O₂ biofuel cell (BFC)-based self-powered sensing platform for visual analysis was developed. The BFC device utilized gold nanoparticle-modified paper fibers as the electrode to wire glucose oxidase (GOx) and bilirubin oxidase for the fabrication of bioanodes and biocathodes. To implement an assay protocol, a target-responsive cargo release system based on mesoporous silica nanocarriers controlled by microRNA-21 (miRNA-21) was designed. During the BFC operation, undesired H₂O₂, the side product of glucose oxidation which would be deleterious for GOx, was generated, leading to inevitable degeneration of BFC performance. On the basis of the H₂O₂-mediated iodide oxidation reaction to form iodine that further modulated the starch chromogenic reaction, undesired H₂O₂ could be effectively removed, resulting in remarkably improved BFC performance as well as providing a means for visual signal readout. Thanks to the dual output signals (maximum power output density or length of blue bar), enhanced analysis reliability and sensitive detection of miRNA-21 over a range of 5 fM to 100 pM were achieved. Moreover, this study demonstrates a proof of concept in visualized BFC-based self-powered systems for sensing applications and provides a blueprint to advance future sensors and analysis devices powered by BFCs in a wide variety of in vitro applications.