Coupled electrochemiluminescent and resonance energy transfer determination of microRNA-141 using functionalized Mxene composite

Signal-on electrochemiluminescence resonance energy transfer biosensor for miRNA-543 based on CRISPR/Cas13a and magnetic separation

In this study, an electrochemiluminescence resonance energy transfer (ECL-RET) biosensor with high sensitivity and strong resistance to interference was constructed based on the CRISPR/Cas13a system and magnetic separation for ovarian cancer biomarker miR-543 detection. Mesoporous silica nanoparticles embedded with Ru(bpy)32+ (Ru@SiO2) have high electrochemiluminescence (ECL) response was chosen as energy donor. Single-stranded DNA S1 containing "rUrU" motif was immobilized on AuNRs (AuNRs-S1), which hybridized with single-stranded DNA S2 modified SAMBs (SAMBs-S2) to form AuNRs-S1/S2-SAMBs complex, this has been used as energy acceptor. In the absence of the target, Cas13a remained inactive, preventing the cleavage of S1, thereby maintaining the association of AuNRs with SAMBs. Then they were added in Ru@SiO2 solution after magnetic separation. The electrostatic adsorption between the negatively charged AuNRs and the positively charged Ru@SiO2 cause the occurrence of ECL-RET and low ECL signal had been detected. When the target was added, Cas13a was activated and resulted in the non-specifically cleaving of S1, so AuNRs detached from SAMBs. After magnetic separation, fewer AuNRs participated in ECL-RET, leading to an enhanced ECL signal detected. The change in ECL intensity (ΔECL) exhibited a linear correlation with the logarithm of miR-543 concentration within the range of 10 fM to 10 nM, with a detection limit of 6.91 fM. The biosensor had been applied to detect miR-543 in clinical samples with high accuracy.

Aggregation-induced ECL strategy based on CuAg nanoclusters/Curdlan-g-PGTMAC for gastric cancer detection

In this work, a novel biosensor based on aggregation-induced luminescence (AIE) of copper-silver alloy nanoclusters (CuAg NCs) has been developed for the detection of gastric cancer marker miRNA-142-3p. The alloy nanoclusters were synthesized by doping Ag ions into Cu NCs as nano-emitters. On the one hand, the doped Ag ions induced Ag-Cu metallophilic interactions, which promoted the relaxation of excited electrons through the radiative pathway. On the other hand, the doped Ag ions can reduce the band gap between the HOMO-LUMO orbitals of the nanoclusters, which decreased the energy consumed for electronic excitation. Therefore, the luminescent signal and stability of CuAg NCs were significantly enhanced. Furthermore, the modification of the permanently positively charged polysaccharide quaternary ammonium salt (Curdlan-g-PGTMAC) on CuAg NCs induced the aggregation-induced electrochemiluminescence (AIECL) effect. The introduction of Curdlan-g-PGTMAC also accelerated the reduction of the co-interaction reagent (S2O82-), which significantly improved the ECL generation efficiency. The ECL response of the CuAg NC-based AIECL biosensor showed a good linear correlation with the concentration of miRNA-142-3p over a wide range from 1 fM to 100 nM with a detection limit as low as 8.8 fM. The ECL biosensor with high sensitivity and wide dynamic range was used for the clinical application of miRNA-142-3p in gastric cancer successfully.

Mechanically stabilized UiO-66-NH2-MB screen printed carbon electrode for high-performance electrochemical ratiometric quantification of miR-21-5p

The ratiometric sensing strategy, which uses dual-signal output, drastically compensates for the background noise and interference from the detection environment, compared to the sensing methods that rely on a single-signal output. However, the stability of the reference signal has become the primary challenge in constructing a ratiometric detection sensor. Therefore, in order to achieve stable ratiometric signal sensing, methylene blue (MB) was encapsulated in the UiO-66-NH2 framework and printed as a reference signal onto a screen-printed carbon electrode (SPCE), facilitating the precise detection of miR-21-5p. Subsequently, based on the ultra-sensitive detection mechanism of catalytic hairpin assembly (CHA), the combination of miR-21-5p with H1 sequence on the Au-deposited SPCE triggered the loop-open of H1. After that, ferrocene-labeled H2 (H2-Fc) and H3-Fc sequences were sequentially added to form a stable "T-shaped" structure, and miR-21-5p was released into the next cycle. Thus, the detection of miR-21-5p was quantified by the current ratio of Fc to MB, obtaining an ultra-low detection limit of 2.7 fM. This ratiometric sensing strategy based on SPCE offers a promising pathway for highly sensitive sensing platforms.

Electrochemiluminescence sensor for organophosphorus pesticides based on the regulation of resonance energy transfer between negative charged gold nanorods and Ru(bpy)32

Combined the electrostatic interaction of the negatively charged gold nanorods (AuNRs) (as acceptor) and Ru(bpy)32+ (as donor), an electrochemiluminescence resonance energy transfer (ECL-RET) sensor was constructed and applied for the detection of organophosphorus pesticides (OPs). Negatively charged AuNRs were synthesized by modifying AuNRs with polystyrene sulfonate (PSS) firstly, which can bind to Ru(bpy)32+ through electrostatic interaction so that the luminophore was absorbed by the acceptor, the resonance energy transfer occurred and only low ECL signal had been detected. Thiocholine can be produced by the hydrolysis process of acetylthiocholine (ATCh) with the help of acetylcholinesterase (AChE), which can bond with PSS-modified AuNRs (PSS-AuNRs) through gold-sulfur interaction, this caused the releasing of the adsorbed Ru(bpy)32+ into the solution and resulting in the restoration of the ECL intensity. However, the activity of AChE was inhibited by OPs, and the recovery process of the ECL signal was thus suppressed as well. In this study, chlorpyrifos was chosen as model target, the results indicated that the correlation between the ECL intensity and the logarithm of chlorpyrifos concentration showed remarkable linearity across 1 ng/mL to 1 mg/mL, achieving a detection limit of 0.51 ng/mL. The proposed system has been utilized for detecting OPs in real samples with satisfied results.

Emerging trends and recent advances in MXene/MXene-based nanocomposites toward electrochemiluminescence sensing and biosensing

Electrochemiluminescence (ECL) sensing systems have surged in popularity in recent years, making significant strides in sensing and biosensing applications. The realization of high-throughput ECL sensors hinges on the implementation of novel signal amplification strategies, propelling the field toward a new era of ultrasensitive analysis. A key strategy for developing advanced ECL sensors and biosensors involves utilizing novel structures with remarkable properties. The past few years have witnessed the emergence of MXenes as a captivating class of 2D materials, with their unique properties leading to exploitation in diverse applications. This review provides a comprehensive summary of the latest advancements in MXene-modified materials specifically engineered for ECL sensing and biosensing applications. We thoroughly analyze the structure, surface functionalization, and intrinsic properties of MXenes that render them exceptionally suitable candidates for the development of highly sensitive ECL sensors and biosensors. Furthermore, this study explores the broad spectrum of applications of MXenes in ECL sensing, detailing their multifaceted roles in enhancing the performance and sensitivity of ECL (bio)sensors. By providing a comprehensive overview, this review is expected to promote progress in related areas.

MXene-based electrochemical devices applied for healthcare applications

The initial part of the review provides an extensive overview about MXenes as novel and exciting 2D nanomaterials describing their basic physico-chemical features, methods of their synthesis, and possible interfacial modifications and techniques, which could be applied to the characterization of MXenes. Unique physico-chemical parameters of MXenes make them attractive for many practical applications, which are shortly discussed. Use of MXenes for healthcare applications is a hot scientific discipline which is discussed in detail. The article focuses on determination of low molecular weight analytes (metabolites), high molecular weight analytes (DNA/RNA and proteins), or even cells, exosomes, and viruses detected using electrochemical sensors and biosensors. Separate chapters are provided to show the potential of MXene-based devices for determination of cancer biomarkers and as wearable sensors and biosensors for monitoring of a wide range of human activities.

MXene-sensitized electrochemiluminescence sensor for thrombin activity detection and inhibitor screening

Thrombin, a crucial enzyme involved in blood coagulation and associated diseases, requires accurate detection of its activity and screening of inhibitors for clinical diagnosis and drug discovery. To address this, an electrochemiluminescence (ECL) method was developed to detect thrombin activity based on the sensitization of Ti₃C₂T_x MXene, which could sensitize the Ru(bpy)₃²⁺ ECL system greatly. The thrombin-cleavable substrate bio-S-G-R-P-V-L-G-C was used as recognizer to evaluate the activity of thrombin. Under the optimal conditions, the limit of detection for thrombin in serum was 83 pU/mL (S/N = 3) with a linear range from 0.1 nU/mL to 1 µU/mL. Moreover, the developed ECL biosensor was employed to screen for thrombin inhibitors from Artemisiae argyi Folium. Four potential thrombin inhibitors (isoquercitrin, nepetin, L-camphor, L-borneol) were screened out with inhibition rates beyond 50%, among which isoquercitrin had the best inhibition rate of 90.26%. Isoquercitrin and nepetin were found to be competitive inhibitors of thrombin, with [Formula: see text] values of 0.91 μM and 2.18 μM, respectively. Molecular docking results showed that these compounds could interact with the active sites of thrombin through hydrogen bonds including ASP189, SER195, GLY216, and GLY219. The electrochemical biosensor constructed provides a new idea for the detection of thrombin activity and screening of its inhibitors.

Advanced growth of 2D MXene for electrochemical sensors

Over the last few years, electroanalysis has made significant advancements, particularly in developing electrochemical sensors. Electrochemical sensors generally include emerging Photoelectrochemical and Electrochemiluminescence sensors, which combine optical techniques and traditional electrochemical bio/non-biosensors. Numerous EC-detecting methods have also been designed for commercial applications to detect biological and non-biological markers for various diseases. Analytical applications have recently focused significantly on one of the novel nanomaterials, the MXene. This material is being extensively investigated for applications in electrochemical sensors due to its unique mechanical, electronic, optical, active functional groups and thermal characteristics. This study extensively discusses the salient features of MXene-based electrochemical sensors, photoelectrochemical sensors, enzyme-based biosensors, immunosensors, aptasensors, electrochemiluminescence sensors, and electrochemical non-biosensors. In addition, their performance in detecting various substances and contaminants is thoroughly discussed. Furthermore, the challenges and prospects the MXene-based electrochemical sensors are elaborated.

In situ synthesis of Cu nanoclusters/CeO2 nanorod as aggregated induced ECL probe for triple-negative breast cancer detection

Cu nanoclusters (NCs) have attracted a lot of attention due to the excellent properties. However, the low luminescence and poor stability limited the Cu NC-based sensing research. In this work, Cu NCs were in situ synthesized on CeO₂ nanorods. On the one hand, the aggregated induced electrochemiluminescence (AIECL) of Cu NCs has been observed on the CeO₂ nanorods. On the other hand, the substrate of CeO₂ nanorods acted as catalysis, which reduced the excitation potential and further enhanced the ECL signal of Cu NCs. It was noticed that CeO₂ nanorods also greatly improved the stability of Cu NCs. The resulted high ECL signals of Cu NCs can be kept constant for several days. Furthermore, MXene nanosheets/Au NPs has been employed as electrode modification materials to construct the sensing platform to detect miRNA-585-3p in triple negative breast cancer tissues. Au NPs@MXene nanosheets not only enlarged the specific interface area of the electrodes and the number of reaction sites, but also modulated electron transfer to amplify the ECL signal of Cu NCs. The biosensor had a low detection limit (0.9 fM) and a wide linear range (1 fM to 1 μM) for the detection of miRNA-585-3p in the clinic tissues.

Towards hospital-on-chip supported by 2D MXenes-based 5th generation intelligent biosensors

Existing public health emergencies due to fatal/infectious diseases such as coronavirus disease (COVID-19) and monkeypox have raised the paradigm of 5th generation portable intelligent and multifunctional biosensors embedded on a single chip. The state-of-the-art 5th generation biosensors are concerned with integrating advanced functional materials with controllable physicochemical attributes and optimal machine processability. In this direction, 2D metal carbides and nitrides (MXenes), owing to their enhanced effective surface area, tunable physicochemical properties, and rich surface functionalities, have shown promising performances in biosensing flatlands. Moreover, their hybridization with diversified nanomaterials caters to their associated challenges for the commercialization of stability due to restacking and oxidation. MXenes and its hybrid biosensors have demonstrated intelligent and lab-on-chip prospects for determining diverse biomarkers/pathogens related to fatal and infectious diseases. Recently, on-site detection has been clubbed with solution-on-chip MXenes by interfacing biosensors with modern-age technologies, including 5G communication, internet-of-medical-things (IoMT), artificial intelligence (AI), and data clouding to progress toward hospital-on-chip (HOC) modules. This review comprehensively summarizes the state-of-the-art MXene fabrication, advancements in physicochemical properties to architect biosensors, and the progress of MXene-based lab-on-chip biosensors toward HOC solutions. Besides, it discusses sustainable aspects, practical challenges and alternative solutions associated with these modules to develop personalized and remote healthcare solutions for every individual in the world.

Two-dimensional transition metal carbides and nitrides (MXenes) based biosensing and molecular imaging

As a "star material", 2D transition metal carbides and/or nitrides (MXenes) have tremendous potential applications in biosensor development and molecular imaging. MXenes have a lot of advantages due to their large specific surface, excellent electrical conductivity, adjustable band gap, and easy modification. MXenes that immobilized with DNA strands, proteins, enzymes, or other bioluminescent materials on the surface, have been used to measure small molecules with extraordinary sensitivity and remarkable limit of detection. This review provides an overview of most recent development in the synthesis, fundamental properties, biosensing, and molecular imaging applications of MXenes. We focused on molecular detection through MXene-based electrochemical properties their challenges and novel opportunities of MXenes in biological applications. This article will provide a guide for researchers who are interested in the application of MXenes biosensors.