Proximity sensitive detection of microRNAs using electrochemical impedance spectroscopy biosensors

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM (I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is  0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

An ultra-sensitive electrochemical biosensor for the detection of procalcitonin in sepsis patients' serum, using a Cu-BHT-based thin film

Procalcitonin (PCT) is a polypeptide produced by the parafollicular cells of the thyroid gland and serves as a vital marker for the diagnosis and treatment of sepsis and other infectious diseases, as well as multiple organ failure, due to its high expression levels in affected patients. This article reports on a highly sensitive electrochemical biosensor based on MOF composite materials, based on Cu-BHT, for detecting PCT levels. The surface of the glassy carbon electrode may have better charge transfer resistance owing to the nano-composite material made of Cu-BHT, chitosan, and AuNPs. At the same time, the anti-PCT antibody may also be covalently bonded to the composite material and measure PCT concentration using electrochemical impedance spectroscopy (EIS). The results of the investigation demonstrate that the sensor's response has excellent linear conjunction with the logarithm of PCT concentration under optimum circumstances. The detection limit (LOD) is 14.579 × 10-9 μg/mL, and the linear range of detection is 10-7 μg/mL to 10-1 μg/mL. Simultaneously, we successfully applied this method to detect serum PCT before and after treatment in different sepsis patients and compared it with chemiluminescence immunoassay. The findings indicate that the proposed method holds promising potential for timely diagnosis and treatment of sepsis patients.

Detection of miR-155 Using Peptide Nucleic Acid at Physiological-like Conditions by Surface Plasmon Resonance and Bio-Field Effect Transistor

MicroRNAs are small ribonucleotides that act as key gene regulators. Their altered expression is often associated with the onset and progression of several human diseases, including cancer. Given their potential use as biomarkers, there is a need to find detection methods for microRNAs suitable for use in clinical setting. Field-effect-transistor-based biosensors (bioFETs) appear to be valid tools to detect microRNAs, since they may reliably quantitate the specific binding between the immobilized probe and free target in solution through an easily detectable electrical signal. We have investigated the detection of human microRNA 155 (miR-155) using an innovative capturing probe constituted by a synthetic peptide nucleic acid (PNA), which has the advantage to form a duplex even at ionic strengths approaching the physiological conditions. With the aim to develop an optimized BioFET setup, the interaction kinetics between miR-155 and the chosen PNA was preliminarily investigated by using surface plasmon resonance (SPR). By exploiting both these results and our custom-made bioFET system, we were able to attain a low-cost, real-time, label-free and highly specific detection of miR-155 in the nano-molar range.

A universal orthogonal imaging platform for living-cell RNA detection using fluorogenic RNA aptamers

MicroRNAs (miRNAs) are crucial regulators of gene expression at the post-transcriptional level, offering valuable insights into disease mechanisms and prospects for targeted therapeutic interventions. Herein, we present a class of miRNA-induced light-up RNA sensors (miLS) that are founded on the toehold mediated principle and employ the fluorogenic RNA aptamers Pepper and Squash as imaging modules. By incorporating a sensor switch to disrupt the stabilizing stem of these aptamers, our design offers enhanced flexibility and convertibility for different target miRNAs and aptamers. These sensors detect multiple miRNA targets (miR-21 and miR-122) with detection limits of 0.48 and 0.2 nM, respectively, while achieving a robust signal-to-noise ratio of up to 44 times. Capitalizing on the distinct fluorescence imaging channels afforded by Pepper-HBC620 (red) and Squash-DFHBI-1T (green), we establish an orthogonal miRNA activation imaging platform, enabling the simultaneous visualization of different intracellular miRNAs in living cells. Our dual-color orthogonal miLS imaging platform provides a powerful tool for sequence-specific miRNA imaging in different cells, opening up new avenues for studying the intricate functions of RNA in living cells.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Sensitive detection of PARP-1 activity by electrochemical impedance spectroscopy based on biomineralization

Poly(ADP)ribose polymerase-1 (PARP-1) has attracted much attention as a tumor marker in recent years. Based on the large negative charge and hyperbranched structure of PARP-1 amplified products (PAR), many detection methods have been established. Herein, we proposed a label-free electrochemical impedance detection method based on the large amount of phosphate groups (PO₄^3-) on the surface of PAR. Although EIS method has high sensitivity, it is not sensitive enough to discern PAR effectively. Therefore, biomineralization was incorporated to increase the resistance value (R_ct) distinctly because of the poor electrical conductivity of CaP. During biomineralization process, plentiful Ca²⁺ was captured by PO₄^3- of PAR through electrostatic interaction, resulting in an increasing R_ct of modified ITO electrode. In contrast, when PRAP-1 was absent, only a little Ca²⁺ was adsorbed on the phosphate backbone of the activating dsDNA. As a result, the biomineralization effect was slight and only a negligible R_ct change occurred. Experiment results showed that R_ct was associated closely with the activity of PARP-1. There was a linear correlation between them when the activity value was in the range of 0.005-1.0 U. The calculated detection limit was 0.003 U. Results of real samples detection and the recovery experiments were satisfactory, indicating the method has an excellent application prospect.

Amplification-free electrochemical biosensor detection of circulating microRNA to identify drug-induced liver injury

Drug-induced liver injury (DILI) is a major challenge in clinical medicine and drug development. There is a need for rapid diagnostic tests, ideally at point-of-care. MicroRNA 122 (miR-122) is an early biomarker for DILI which is reported to increase in the blood before standard-of-care markers such as alanine aminotransferase activity. We developed an electrochemical biosensor for diagnosis of DILI by detecting miR-122 from clinical samples. We used electrochemical impedance spectroscopy (EIS) for direct, amplification free detection of miR-122 with screen-printed electrodes functionalised with sequence specific peptide nucleic acid (PNA) probes. We studied the probe functionalisation using atomic force microscopy and performed elemental and electrochemical characterisations. To enhance the assay performance and minimise sample volume requirements, we designed and characterised a closed-loop microfluidic system. We presented the EIS assay's specificity for wild-type miR-122 over non-complementary and single nucleotide mismatch targets. We successfully demonstrated a detection limit of 50 pM for miR-122. Assay performance could be extended to real samples; it displayed high selectivity for liver (miR-122 high) comparing to kidney (miR-122 low) derived samples extracted from murine tissue. Finally, we successfully performed an evaluation with 26 clinical samples. Using EIS, DILI patients were distinguished from healthy controls with a ROC-AUC of 0.77, a comparable performance to qPCR detection of miR-122 (ROC-AUC: 0.83). In conclusion, direct, amplification free detection of miR-122 using EIS was achievable at clinically relevant concentrations and in clinical samples. Future work will focus on realising a full sample-to-answer system which can be deployed for point-of-care testing.

An ultrasensitive and disposable electrochemical aptasensor for prostate-specific antigen (PSA) detection in real serum samples

In this study, we constructed a disposable indium tin oxide polyethylene terephthalate film (ITO-PET)-based electrochemical aptasensor for analyzing prostate-specific antigen (PSA), one of the most important biomarkers of prostate cancer. Because of their clinical importance, building PSA biosensing systems with high sensitivity and stability is essential. However, it still presents significant difficulties, such as low detection limits. We designed a platform to covalently bind the amino-terminated aptamer by modifying the ITO-PET surface with carboxyethylsilanetriol (CTES) to obtain a self-assembled monolayer (SAM). We also evaluated the potential for use in real human serum samples by investigating the optimal operating conditions and analytical performance characteristics of the developed biosensor. The design we present here exhibits excellent precision, with a limit of detection (LOD) as low as 8.74 fg/mL PSA. The broad linear detection range of the biosensor under optimal conditions was determined as 1.0-1500 fg/mL. The dissociation constant (K_d) for the aptamer was also calculated as 46.28 ± 5.63 nM by evaluating the impedimetric response as a function of PSA concentration. The aptasensor displayed considerable repeatability (1.3% RSD) and reproducibility (7.51% RSD) and good storage stability (98.34% of the initial activity for 8 weeks). Additionally, we demonstrated that the technique we developed was quite efficient in estimating the kinetics of aptamer-analyte interactions by determining the K_d and single-frequency impedance (SFI) data. In conclusion, we proposed a selective and sensitive biosensor with the potential for clinical application and superior performance in real serum samples.

Amplification Free Detection of SARS-CoV-2 Using Multi-Valent Binding

We present the development of electrochemical impedance spectroscopy (EIS)-based biosensors for sensitive detection of SARS-CoV-2 RNA using multi-valent binding. By increasing the number of probe-target binding events per target molecule, multi-valent binding is a viable strategy for improving the biosensor performance. As EIS can provide sensitive and label-free measurements of nucleic acid targets during probe-target hybridization, we used multi-valent binding to build EIS biosensors for targeting SARS-CoV-2 RNA. For developing the biosensor, we explored two different approaches including probe combinations that individually bind in a single-valent fashion and the probes that bind in a multi-valent manner on their own. While we found excellent biosensor performance using probe combinations, we also discovered unexpected signal suppression. We explained the signal suppression theoretically using inter- and intra-probe hybridizations which confirmed our experimental findings. With our best probe combination, we achieved a LOD of 182 copies/μL (303 aM) of SARS-CoV-2 RNA and used these for successful evaluation of patient samples for COVID-19 diagnostics. We were also able to show the concept of multi-valent binding with shorter probes in the second approach. Here, a 13-nt-long probe has shown the best performance during SARS-CoV-2 RNA binding. Therefore, multi-valent binding approaches using EIS have high utility for direct detection of nucleic acid targets and for point-of-care diagnostics.