On-Electrode Synthesis of Shape-Controlled Hierarchical Flower-Like Gold Nanostructures for Efficient Interfacial DNA Assembly and Sensitive Electrochemical Sensing of MicroRNA

Amplification-Free Analysis of Bladder Cancer MicroRNAs on Wrinkled Silica Nanoparticles with DNA-Functionalized Quantum Dots

Bladder cancer (BC) occurrence and progression are accompanied by alterations in microRNAs (miRNAs) expression levels. Simultaneous detection of multiple miRNAs contributes to the accuracy and reliability of the BC diagnosis. In this work, wrinkled silica nanoparticles (WSNs) were applied as the microreactor for multiplex miRNAs analysis without enzymes or nucleic acid amplification. Conjugated on the surface of WSNs, the S9.6 antibody was adopted as the universal module for binding DNA/miRNA duplexes, regardless of their sequence. Furthermore, single-stranded DNA (ssDNA) was labeled with quantum dots (QDs) for identifying a given miRNA to form QDs-ssDNA/miRNA, which enabled the specific capture of the corresponding QDs on the wrinkled surface of WSNs. Based on the detection of fluorescence signals that were ultimately focused on WSNs, target miRNAs could be sensitively identified to a femtomolar level (5 fM) with a wide dynamic range of up to 6 orders of magnitude. The proposed strategy achieved high specificity to obviously distinguish single-base mutation sequences and possessed multiplex assay capability. Moreover, the assay exhibited excellent practicability in the multiplex detection of miRNAs in clinical serum specimens.

Machine learning-powered electrochemical aptasensor for simultaneous monitoring of di(2-ethylhexyl) phthalate and bisphenol A in variable pH environments

Plastic waste is a pernicious environmental pollutant that threatens ecosystems and human health by releasing contaminants including di(2-ethylhexyl) phthalate (DEHP) and bisphenol A (BPA). Therefore, a machine-learning (ML)-powered electrochemical aptasensor was developed in this study for simultaneously detecting DEHP and BPA in river waters, particularly to minimize the electrochemical signal errors caused by varying pH levels. The aptasensor leverages a straightforward and effective surface modification strategy featuring gold nanoflowers to achieve low detection limits for DEHP and BPA (0.58 and 0.59 pg/mL, respectively), excellent specificity, and stability. The least-squares boosting (LSBoost) algorithm was introduced to reliably monitor the targets regardless of pH; it employs a layer that adjusts the number of multi-indexes and the parallel learning structure of an ensemble model to accurately predict concentrations by preventing overfitting and enhancing the learning effect. The ML-powered aptasensor successfully detected targets in 12 river sites with diverse pH values, exhibiting higher accuracy and reliability. To our knowledge, the platform proposed in this study is the first attempt to utilize ML for the simultaneous assessment of DEHP and BPA. This breakthrough allows for comprehensive investigations into the effects of contamination originating from diverse plastics by eliminating external interferent-caused influences.

Lung Cancer Cell-Derived Exosome Detection Using Electrochemical Approach towards Early Cancer Screening

Lung cancer is one of the deadliest cancers worldwide due to the inability of existing methods for early diagnosis. Tumor-derived exosomes are nano-scale vesicles released from tumor cells to the extracellular environment, and their investigation can be very useful in both biomarkers for early cancer screening and treatment assessment. This research detected the exosomes via an ultrasensitive electrochemical biosensor containing gold nano-islands (Au-NIs) structures. This way, a high surface-area-to-volume ratio of nanostructures was embellished on the FTO electrodes to increase the chance of immobilizing the CD-151 antibody. In this way, a layer of gold was first deposited on the electrode by physical vapor deposition (PVD), followed by thermal annealing to construct primary gold seeds on the surface of the electrode. Then, gold seeds were grown by electrochemical deposition through gold salt. The cell-derived exosomes were successfully immobilized on the FTO electrode through the CD-151 antibody, and cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods were used in this research. In the CV method, the change in the current passing through the working electrode is measured so that the connection of exosomes causes the current to decrease. In the EIS method, surface resistance changes were investigated so that the binding of exosomes increased the surface resistance. Various concentrations of exosomes in both cell culture and blood serum samples were measured to test the sensitivity of the biosensor, which makes our biosensor capable of detecting 20 exosomes per milliliter.

Biological Recognition-Based Electrochemical Aptasensor for Point-of-Care Detection of cTnI

As a "gold standard biomarker", cardiac troponin I (cTnI) is widely used to diagnose acute myocardial infarction (AMI). For an early clinical diagnosis of AMI, it is necessary to develop a facile, fast and on-site device for cTnI detection. According to this demand, a point-of-care electrochemical aptasensor was developed for cTnI detection by coupling the advantages of screen-printed carbon electrode (SPCE) with those of an aptamer. Thiol and methylene blue (MB) co-labelled aptamer (MB-Apt-SH) was assembled on the surface of hierarchical flower-like gold nanostructure (HFGNs)-decorated SPCE (SPCE-HFGNs) to recognize and analyze cTnI. In the presence of cTnI, the specific biological recognition reaction between cTnI and aptamer caused the decrease in electrochemical signal. Under the optimal condition, this designed aptasensor showed wide linear range (10 pg/mL-100 ng/mL) and low detection limit for (8.46 pg/mL) for cTnI detection with high selectivity and stability. More importantly, we used a mobile phone coupled with a simple APP to efficiently detect cTnI in 10 μL 100% human serum samples, proving that this aptasensor has a promising potential in point-of-care testing.

Electrochemical H2O2 sensor based on a Au nanoflower-graphene composite for anticancer drug evaluation

Reliable H₂O₂ sensors for in situ cellular monitoring under drug stimulation can be developed as a powerful and versatile tool for drug evaluation. Herein, a novel electrochemical biosensor capable of detecting and quantifying H₂O₂ was fabricated by graphene and shape-controlled gold nanostructures. With the help of polyelectrolytes, gold exhibited hierarchical flower-like nanostructures. This kind of nanozyme material exhibited a prominent electrochemical response for H₂O₂. Electrocatalytic activity for H₂O₂ reduction with high sensitivity (5.07◊10^-4 mA μmol L^-1 cm^-2) and good detection capability (the lowest detection limit is 4.5 μmol L^-1 (S/N = 3)) were achieved. This electrochemical biosensor was successfully used to measure the concentration of H₂O₂ released from HepG2 hepatoma cells. Ascorbic acid (AA) and Camellia nitidissima Chi saponins (CNCS) were selected as model drugs, and their anticancer activities were compared by in situ monitoring of H₂O₂. Interestingly, the electrochemical sensor showed remarkable sensitivity, accuracy, and rapidity compared with the traditional enzymatic detection kit. In brief, the as-synthesized nanostructured H₂O₂ sensors can be applied to assess the antitumor properties of candidate drugs and inspire developments for personalized health care monitoring and cancer treatment.

Advances in Electrochemical Biosensor Technologies for the Detection of Nucleic Acid Breast Cancer Biomarkers

Breast cancer is the second leading cause of cancer deaths in women worldwide; therefore, there is an increased need for the discovery, development, optimization, and quantification of diagnostic biomarkers that can improve the disease diagnosis, prognosis, and therapeutic outcome. Circulating cell-free nucleic acids biomarkers such as microRNAs (miRNAs) and breast cancer susceptibility gene 1 (BRCA1) allow the characterization of the genetic features and screening breast cancer patients. Electrochemical biosensors offer excellent platforms for the detection of breast cancer biomarkers due to their high sensitivity and selectivity, low cost, use of small analyte volumes, and easy miniaturization. In this context, this article provides an exhaustive review concerning the electrochemical methods of characterization and quantification of different miRNAs and BRCA1 breast cancer biomarkers using electrochemical DNA biosensors based on the detection of hybridization events between a DNA or peptide nucleic acid probe and the target nucleic acid sequence. The fabrication approaches, the biosensors architectures, the signal amplification strategies, the detection techniques, and the key performance parameters, such as the linearity range and the limit of detection, were discussed.

A novel electrochemical biosensor based on signal amplification of Au HFGNs/PnBA-MXene nanocomposite for the detection of miRNA-122 as a biomarker of breast cancer

Cancer is one of the leading causes of death worldwide and a crisis for global health. Breast cancer is the second most common cancer globally. In the perusal, a novel electrochemical biosensor amplified with hierarchical flower-like gold, poly (n-butyl acrylate), and MXene (AuHFGNs/PnBA-MXene) nanocomposite and activated by highly special antisense ssDNA (single-stranded DNA) provide a promising alternative for miRNA-122 detection as a biomarker of breast cancer. The biosensor presented a detection limit of 0.0035 aM (S/N = 3) with a linear range from 0.01 aM to 10 nM. The platform was tried on 20 breast cancer miRNAs extracted from actual serum specimens (10 positives and 10 negatives). Founded on the quantitatively obtained outcomes and statistic analysis (t-test, box-graph, receiver performance characteristic curve, and cut-off amount), the biosensor showed a meaningful discrepancy between the native and positive groups with 100% specificity and 100% sensitivity. While, RT-qPCR showed less specificity and sensitivity (70% specificity, 100% sensitivity) than the proposed biosensor. To assess the quantitative capacity and biosensor detection limit for clinical tests, the biosensor diagnosis performance for continually diluted miRNA extracted from patients was compared to that gained by RT-qPCR results, indicating that the biosensor detection limit was lower than RT-qPCR. ssDNA/AuHFGN/PnBA-MXene/GCE displayed little cross-reaction with other sequences and also showed desirable stability, reproducibility, and specificity and stayed stable until 32 days. As a result, the designed biosensor can perform as a hopeful method for diagnosis applications.

Label-free electrochemical detection of cancer biomarkers DNA and anti-p53 at tin oxide quantum dot-gold-DNA nanoparticle modified electrode

Lung cancer is one of the deadliest types of cancer and accounts for 8.1% of all cancer related deaths. To prevent a growing death rate, it is crucial to identify lung cancer at an early stage by single polynucleotide morphism detection. In this paper, we present a novel label-free electrochemical biosensor based on composites of tin oxide quantum dots and gold nanoparticles (SnO₂-QD-Au) for the sensitive and precise detection of lung cancer DNA. The SnO₂-QD and SnO₂-QD-Au nanoparticles were characterized using Scanning and Transmission Electron Microscopes (SEM and TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy (UV), Fourier transmission infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Gold thiol covalent bonding was used for immobilising probe DNA on the surface of SnO₂-QD-Au nanoparticles followed by target DNA hybridization and detected electrochemically in presence of 1 mM [Fe(CN₆)]^3-/4-as a redox couple probe. Under ideal circumstances, the sensor showed the lowest detection limit of 3.2 × 10^-20 M with a linear range of 1 × 10^-6 - 1 × 10^-20 M. Additionally, the sensing method was applied to find a cancer biomarker, Anti-P53 antibody.

Atomic layer deposition (ALD)-constructed TaS2nanoflakes for cancer-related nucleolin detection

Sensitive detection of nucleolin (NCL) is of great significance for the early diagnosis of cancer. In this work, as a new type of two-dimensional (2D) transition metal dichalcogenides (TMDCs), TaS₂nanoflakes (NFs) were precisely constructed by atomic layer deposition (ALD) on carbon fiber paper (CFP) with high specific surface area.In situobservation showed that the nucleation and growth of TaS₂nanoflakes were precisely controlled by the number of ALD cycles, thereby regulating their electrochemical properties. The electrochemical performance of TaS₂NFs was observed in depth, and compared with that of traditional 2D TMDCs. Due to the high surface area and conductivity, anodic/cathodic current of ∼1570μA of TaS₂NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on ALD-constructed TaS₂NFs/CFP for cancer-related NCL detection was fabricated. Due to the excellent electrochemical performance of TaS₂NFs/CFP, ultrasensitive detection of NCL in the linear range of 0.1 pM-10 nM with a detection limit of 0.034 pM was achieved.

Direct fabrication of NbS2 nanoflakes on carbon fibers by atomic layer deposition for ultrasensitive cardiac troponin I detection

The sensitive detection of cardiac troponin I (cTnI) is of great significance for the early diagnosis of acute myocardial infarction (AMI). Herein, in order to fabricate an electrochemical biosensor for ultrasensitive cTnI detection, atomic layer deposition (ALD) was employed to directly deposit NbS₂ nanoflakes (NFs) on carbon fiber paper (CFP). Due to the self-limiting reaction of ALD, NbS₂NFs were deposited uniformly and accurately on the surface of carbon fibers by controlling the number of ALD cycles, which ensured ultrasensitive detection. Precise regulation of the nanoscale morphology and electrochemical performance of NbS₂ nanoflakes via ALD cycles was observed in depth. Owing to the high surface area and conductivity, an anodic/cathodic current of ∼3.01 mA of NbS₂NFs/CFP can be obtained. Subsequently, an electrochemical biosensor based on the excellent performance of NbS₂NFs/CFP was fabricated. The ultrasensitive detection of cTnI in a linear range of 1 fM to 0.1 nM with a detection limit of 0.32 fM was achieved.

Dual-Modal Immunosensor Made with the Multifunction Nanobody for Fluorescent/Colorimetric Sensitive Detection of Aflatoxin B1 in Maize

In recent years, dual-modal immunosensors based on synthetic nanomaterials have provided accurate and sensitive detection. However, preparation of nanomaterial probes can be time-consuming, laborious, and not limited to producing inactive and low-affinity antibodies. These challenges can be addressed through the multifunction nanobody without conjugation. In this study, a nanobody-enhanced green fluorescent (Nb26-EGFP) was novel produced with a satisfactory affinity and fluorescent properties. Then, a dual-modal fluorescent/colorimetric immunosensor was constructed using the Nb26-EGFP-gold nanoflowers (AuNFs) composite as a probe, to detect the aflatoxin B₁ (AFB₁). In the maize matrix, the proposed immunosensor showed high sensitivity with a limit of detection (LOD) of 0.0024 ng/mL and a visual LOD of 1 ng/mL, which is 20-fold and 325-fold compared with the Nb26-EGFP-based single-modal immunosensor and original nanobody Nb26-based immunoassay. The performance of the dual-modal assay was validated by a high-performance liquid chromatography method. The recoveries were between 83.19 and 108.85%, with the coefficients of variation below 9.43%, indicating satisfied accuracy and repeatability. Overall, the novel Nb26-EGFP could be used as the detection probe, and the dual-modal immunosensor could be used as a practical detection method for AFB₁ in real samples.

Morphology-Tuned Electrochemical Immunosensing of a Breast Cancer Biomarker Using Hierarchical Palladium Nanostructured Interfaces

Metallic nanostructures are considered attractive candidates for designing novel biosensors due to their enormously significant surface area, accelerated kinetics, and improved affinity. Controllable morphological tuning of metallic nanostructures on sensing interfaces is crucial for attaining clinically relevant sensitivity and exquisite selectivity in a complex biological environment. Therefore, a facile, convenient, and robust one-step electroreduction method was employed to develop different morphological variants of palladium (Pd) nanostructures supported onto oxidized carbon nanotubes to facilitate label-free electrochemical immunosensing of HER2. The morphological and structural attributes of the synthesized Pd nanostructures were thoroughly investigated using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy techniques. In-depth electrochemical investigations revealed an intimate correlation between the nanostructured sensor and electrochemical response, suggesting the suitability of hierarchical palladium nanostructures supported onto carbon nanotubes [Pd(-0.1 V)/CNT] for sensitive detection of HER2. The high surface area of hierarchical Pd nanostructures enabled an ultrasensitive electrochemical response toward HER2 (detection limit: 1 ng/mL) with a wide detection range of 10 to 100 ng/mL. The ease of surface modification, sensitivity, and reliable electrochemical response in human plasma samples suggested the enormous potential of Pd nanostructuring for chip-level point-of-care screening of HER2-positive breast cancer patients.

Introduction of Nanomaterials to Biosensors for Exosome Detection: Case Study for Cancer Analysis

Exosomes have been gaining attention for early cancer diagnosis owing to their biological functions in cells. Several studies have reported the relevance of exosomes in various diseases, including pancreatic cancer, retroperitoneal fibrosis, obesity, neurodegenerative diseases, and atherosclerosis. Particularly, exosomes are regarded as biomarkers for cancer diagnosis and can be detected in biofluids, such as saliva, urine, peritoneal fluid, and blood. Thus, exosomes are advantageous for cancer liquid biopsies as they overcome the current limitations of cancer tissue biopsies. Several studies have reported methods for exosome isolation, and analysis for cancer diagnosis. However, further clinical trials are still required to determine accurate exosome concentration quantification methods. Recently, various biosensors have been developed to detect exosomal biomarkers, including tumor-derived exosomes, nucleic acids, and proteins. Among these, the exact quantification of tumor-derived exosomes is a serious obstacle to the clinical use of liquid biopsies. Precise detection of exosome concentration is difficult because it requires clinical sample pretreatment. To solve this problem, the use of the nanobiohybrid material-based biosensor provides improved sensitivity and selectivity. The present review will discuss recent progress in exosome biosensors consisting of nanomaterials and biomaterial hybrids for electrochemical, electrical, and optical-based biosensors.

A Portable Biosensor Based on Au Nanoflower Interface Combined with Electrochemical Immunochromatography for POC Detection of Prostate-Specific Antigen

Serum prostate-specific antigen (PSA) is a widely used for the detection of prostate cancer and is considered the most reliable biomarker. However, the currently reported detection methods cannot achieve rapid monitoring. Here, we report a novel electrochemical immunochromatography (EIC) system for clinically accurate PSA detection. First, we constructed a carbon interface modified with gold nanoflowers (Au NFs) based on screen-printed carbon electrodes (SPCE), which acted as nanostructures with larger specific surface area that increased the number of PSA capture antibodies and can further improve detection signal-to-noise (S/N) ratio. Then, we fabricated detection chips by combining the SPCE/Au NFs with EIC. Under optimized conditions, the proposed biosensor exhibits high accuracy, taking only 15 minutes to complete detection. By measuring the levels of PSA in clinical blood samples, the biosensor can successfully discriminate clinically diagnosed prostate cancer patients from healthy controls.

Sensitive and specific clinically diagnosis of SARS-CoV-2 employing a novel biosensor based on boron nitride quantum dots/flower-like gold nanostructures signal amplification

The sudden increase of the COVID-19 outbreak and its continued growth with mutations in various forms has created a global health crisis as well as devastating social and economic effects over the past two years. In this study, a screen-printed carbon electrode reinforced with boron nitride quantum dots/flower-like gold nanostructures (BNQDs/FGNs/SPCE) and functionalized by highly specific antisense DNA oligonucleotide presents an alternative and promising solution for targeting SARS-CoV-2 RNA without nucleic acid amplification. The platform was tested on 120 SARS-CoV-2 RNA isolated from real clinical samples (60 positive and 60 negative confirmed by conventional RT-PCR method). Based on obtained quantitative results and statistical analysis (box-diagram, cutoff value, receiver operating characteristic curve, and t-test), the biosensor revealed a significant difference between the two positive and negative groups with 100% sensitivity and 100% specificity. To evaluate the quantitation capacity and detection limit of the biosensor for clinical trials, the detection performance of the biosensor for continuously diluted RNA isolated from SARS-CoV-2-confirmed patients was compared to those obtained by RT-PCR, demonstrating that the detection limit of the biosensor is lower than or comparable to that of RT-PCR. The ssDNA/BNQDs/FGNs/SPCE showed negligible cross-reactivity with RNA fragments isolated from Influenza A (IAV) clinical samples and also remained stable for up to 14 days. In conclusion, the fabricated biosensor may serve as a promising tool for point-of-care applications.

Sensitive electrochemiluminescence analysis of lung cancer marker miRNA-21 based on RAFT signal amplification

An electrochemiluminescence approach based on surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) was developed for miRNA-21 detection for the first time. The SI-RAFT polymerization generates polymer chains with functional groups that are used to recruit luminol, enabling strong ECL signal output with low concentrations of miRNA-21, and greatly improving the detection sensitivity.

Recent Progresses in Electrochemical DNA Biosensors for MicroRNA Detection

MicroRNAs (miRNAs), as the small, non-coding, evolutionary conserved, and post-transcriptional gene regulators of the genome, have been highly associated with various diseases such as cancers, viral infections, and cardiovascular diseases. Several techniques have been established to detect miRNAs, including northern blotting, real-time polymerase chain reaction (RT-PCR), and fluorescent microarray platform. However, it remains a significant challenge to develop sensitive, accurate, rapid, and cost-effective methods to detect miRNAs due to their short size, high similarity, and low abundance. The electrochemical biosensors exhibit tremendous potential in miRNA detection because they satisfy feature integration, portability, mass production, short response time, and minimal sample consumption. This article reviewed the working principles and signal amplification strategies of electrochemical DNA biosensors summarized the recent improvements. With the development of DNA nanotechnology, nanomaterials and biotechnology, electrochemical DNA biosensors of high sensitivity and specificity for microRNA detection will shortly be commercially accessible.

Simultaneous detection of dual biomarkers using hierarchical MoS2 nanostructuring and nano-signal amplification-based electrochemical aptasensor toward accurate diagnosis of prostate cancer

Accurate and reliable quantification of tumor biomarkers in clinical samples is of vital importance for early stage diagnosis and treatment of cancer. However, a poor specificity of prostate specific antigen (PSA) testing alone fostering overdetection and overtreatment, remains a great controversy in prostate cancer (PCa) screening. Here we report an electrochemical aptasensor using hierarchical MoS₂ nanostructuring and SiO₂ nano-signal amplification for simultaneous detection of dual PCa biomarkers, PSA and sarcosine, to enhance the diagnostic performance of PCa. In this strategy, hierarchical flower-like MoS₂ nanostructures as functional interface accelerated intermolecular accessibility and improved DNA hybridization efficiency. Moreover, the spherical SiO₂ nanoprobe that conjugated with both electroactive tags and DNA probes, allowed effective electrochemical signal amplification. By deliberately designing different hybridization modes, we individually implemented the optimization of PSA and sarcosine sensing system. Based on this, simultaneous determination of PSA and sarcosine was achieved, with limit of detection (LOD) down to 2.5 fg/mL and 14.4 fg/mL, respectively, as well as excellent selectivity. More importantly, using this approach, we could directly differentiate cancer patients with healthy ones for clinical serum samples. The ultrasensitive biosensor provides single-step analysis with simple operation and a small sample volume (∼12 μL), shedding new light on accurate diagnosis and early-detection of cancer in clinical applications.

Construction of a Au@MoS2 composite nanosheet biosensor for the ultrasensitive detection of a neurotransmitter and understanding of its mechanism based on DFT calculations

MoS₂ nanosheets can be applied as electrochemical biosensors to selectively and sensitively respond to the surrounding environment and detect various biomolecules due to their large specific surface area and unique physicochemical properties. In this paper, single-layer or few-layer MoS₂ nanosheets were prepared by an improved liquid phase stripping method, and then combining the unique material characteristics of MoS₂ and the metallic property of Au nanoparticles (AuNPs), Au@MoS₂ composite nanosheets were synthesized based on MoS₂ nanosheets. Then, the structure and properties of MoS₂ nanosheets and Au@MoS₂ composite nanosheets were comprehensively characterized. The results proved that AuNPs were successfully loaded on MoS₂ nanosheets. At the same time, on the basis of the successful preparation of Au@MoS₂ composite nanosheets, an electrochemical biosensor targeting dopamine was successfully constructed by cyclic voltammetry. The linear detection range was 0.5–350 μM, and the detection limit was 0.2 μM. The high-sensitive electrochemical detection of dopamine has been achieved, which provides a new idea for the application of MoS₂-based nanomaterials in the biosensing of neurotransmitters. In addition, density functional theory (DFT) was used to explore the electrochemical performance of Au@MoS₂ composite nanosheets. The results show that the adsorption of Au atoms on the MoS₂ 2D structure improves the conductivity of MoS₂ nanosheets, which theoretically supports the possibilities of its application as a platform for the ultrasensitive detection of neurotransmitters or other biomolecules in the field of disease diagnosis.

An electrochemical biosensor based on Au@MoS₂ composite nanosheets was successfully prepared for the high-sensitivity detection of dopamine.

Delineating the Role of Tailored Gold Nanostructures at the Biointerface

Gold (Au) has emerged as a superior element, because of its widespread applications in electronic and medical fields. The desirable physical, chemical, optical, and inherent enzyme-like properties of Au are efficiently exploited for detection, diagnostic, and therapeutic purposes. Au offers a unique advantage of fabricating gold nanostructures (GNS) having exact physical, chemical, optical, and enzyme-like properties required for the specific biomedical application. In this Review, the emerging trend of GNS for various biomedical applications is highlighted. Some notable structural and chemical modifications achieved for the detection of biomolecules, pathogens, diagnosis of diseases, and therapeutic applications are discussed in brief. The limitations of GNS during biomedical usage are highlighted and the way forward to overcome these limitations are discussed.

Accelerated Electron Transfer in Nanostructured Electrodes Improves the Sensitivity of Electrochemical Biosensors

Electrochemical biosensors hold the exciting potential to integrate molecular detection with signal processing and wireless communication in a miniaturized, low-cost system. However, as electrochemical biosensors are miniaturized to the micrometer scale, their signal-to-noise ratio degrades and reduces their utility for molecular diagnostics. Studies have reported that nanostructured electrodes can improve electrochemical biosensor signals, but since the underlying mechanism remains poorly understood, it remains difficult to fully exploit this phenomenon to improve biosensor performance. In this work, electrochemical aptamer biosensors on nanoporous electrode are optimized to achieve improved sensitivity by tuning pore size, probe density, and electrochemical measurement parameters. Further, a novel mechanism in which electron transfer is physically accelerated within nanostructured electrodes due to reduced charge screening, resulting in enhanced sensitivity is proposed and experimentally validated. In concert with the increased surface areas achieved with this platform, this newly identified effect can yield an up to 24-fold increase in signal level and nearly fourfold lower limit of detection relative to planar electrodes with the same footprint. Importantly, this strategy can be generalized to virtually any electrochemical aptamer sensor, enabling sensitive detection in applications where miniaturization is a necessity, and should likewise prove broadly applicable for improving electrochemical biosensor performance in general.

Redox Host-Guest Nanosensors Installed with DNA Gatekeepers for Immobilization-Free and Ratiometric Electrochemical Detection of miRNA

Electrochemical nanosensors by integrating functional nucleic acids and nanomaterials hold a great promise in the fast detection of biomarkers, yet the current systems possess limitations on the accessibility of target-probe and probe-electrode interactions and the repeatability of detection. Herein, a host-guest assembly strategy is developed to build redox nanosensors for an immobilization-free and ratiometric electrochemical detection system. Specifically, electroactive molecule (E_m ) guests are loaded in porous hosts of polydopamine nanoparticles (MPDA) to act as dual-signal redox reporters. Hybrid DNA probes of G-quadruplex and a single-stranded anchor DNA are installed as gatekeepers for sealing the mesopores. Thereby, miRNA triggered E_m release by strand displacement reactions and the homogeneous transportation of the hosts/guests to the electrode facilitate the generation of reference signal/response signal at different potentials. Concomitantly applied NIR irradiation boosts the electron transfer from MPDA to the electrode and results in a tenfold increase in the reference signal. Finally, the sensing system through the differential pulse voltammetry method achieves a highly repeatable detection (relative standard deviation 3.8%) of miRNA with a lower detection limit (362 × 10^-15 m). This attractive system paves the way for rational designs of advanced electrochemical biosensors and smart diagnosis.

Evolution of nucleic acids biosensors detection limit III

This review is an update of two previous ones focusing on the limit of detection of electrochemical nucleic acid biosensors allowing direct detection of nucleic acid target (miRNA, mRNA, DNA) after hybridization event. A classification founded on the nature of the electrochemical transduction pathway is established. It provides an overall picture of the detection limit evolution of the various sensor architectures developed during the last three decades and a critical report of recent strategies.

Challenges and Opportunities for Clustered Regularly Interspaced Short Palindromic Repeats Based Molecular Biosensing

Clustered regularly interspaced short palindromic repeats, CRISPR, has recently emerged as a powerful molecular biosensing tool for nucleic acids and other biomarkers due to its unique properties such as collateral cleavage nature, room temperature reaction conditions, and high target-recognition specificity. Numerous platforms have been developed to leverage the CRISPR assay for ultrasensitive biosensing applications. However, to be considered as a new gold standard, several key challenges for CRISPR molecular biosensing must be addressed. In this paper, we briefly review the history of biosensors, followed by the current status of nucleic acid-based detection methods. We then discuss the current challenges pertaining to CRISPR-based nucleic acid detection, followed by the recent breakthroughs addressing these challenges. We focus upon future advancements required to enable rapid, simple, sensitive, specific, multiplexed, amplification-free, and shelf-stable CRISPR-based molecular biosensors.

Enhanced electrochemiluminescence ratiometric cytosensing based on surface plasmon resonance of Au nanoparticles and nanosucculent films

Ramos cells are human Burkitt's lymphoma cells, which are a kind of cancer cells to facilitate the monitoring of the relevant biological processes of cancers. Sensitive and accurate detection of Ramos cells using emerging ratiometric ECL biosensing technology shows increasing importance, however, the target analytes of current ratiometric ECL biosensors are mainly limited to DNA/RNA or proteins. In this study, we proposed a dual-potential ratiometric sensing strategy for the electrochemiluminescence detection of Ramos cells based on two types of electrochemiluminescence (ECL)-responding molecular. Au nanosucculent films (AuNFs) were electrodeposited on the fluorine doped tin oxide (FTO) electrode to increase the effective area of the electrode for more efficient assembly of DNA and effectively improving the conductivity of the sensing interfaces. In the presence of Ramos cells, aptamers capped with Au@luminol would conjugate with Ramos cells and then remove from AuNFs, accompanying the decrease of ECL signal from Au@luminol. Then, Au-DNA was captured and alternately hybridized with DNA-modified CdS nanocrystals (NCs) on the surface of AuNFs with the formation of a super reticulate structure. The reticulate structure not only raised another identified ECL signal from CdS NCs but also greatly promoted its ECL intensity from the surface plasmon resonance originating from Au NPs. The value of log (ECL_CdS/ECL_luminol) and the logarithm of the number of cells exhibit considerable linear relation ranging from 80 to 8 × 10⁵ cells mL^-1 with a low detection limit of 20 cells mL^-1 (S/N = 3). The selectivity and specificity of this dual-potential ECL sensor showed good performance and indicated considerable promise in avoiding false-positive results in detection.

A photoelectrochemical sensor based on a reliable basic photoactive matrix possessing good analytical performance for miRNA-21 detection

The basic photoactive matrixes on transparent electrodes are essential for the performance of photoelectrochemical (PEC) biosensors. Herein, we demonstrate an optimized fabrication strategy toward a reliable ITO/TiO2/AuNP photoanode by sequential deposition of TiO2/Au nanoparticles (Au NPs) on indium tin oxide (ITO) substrates. The identified fabrication conditions include spin-coating tetraisopropyl titanate on ITO slices followed by in situ electrodeposition of Au NPs and finally the thermal annealing treatment. By the conjugation of the thiolated hairpin NH2-DNA sequence and CdTe quantum dots (QDs) onto the thus-prepared photoanodes, a novel PEC sensor for the ultrasensitive detection of miRNA was constructed. The proposed PEC sensor offered advantages including simple structure, storage stability and excellent detection reproducibility as well as sensitivity and specificity toward miRNA-21. Finally, we found that this PEC displayed a broad detection linear range of 1.0 fM to 1.0 nM with a low detection limit of 0.37 fM. This PEC sensor can also excellently discriminate the mismatched miRNA. Moreover, the PEC sensor also showed a satisfactory result in normal human serum sample analysis. These findings emphasized the importance of basic photoactive matrixes for the fabrication of PEC sensors, providing solid fundamental insights for future application of metal oxide substrates for other PEC applications, especially PEC biosensors.

Recent trends in application of nanomaterials for the development of electrochemical microRNA biosensors

The biology of the late twentieth century was marked by the discovery in 1993 of a new class of small non-coding ribonucleic acids (RNAs) which play major roles in regulating the translation and degradation of messenger RNAs. These small RNAs (18-25 nucleotides), called microRNAs (miRNAs), are implied in several biological processes such as differentiation, metabolic homeostasis, or cellular apoptosis and proliferation. The discovery in 2008 that the presence of miRNAs in body fluids could be correlated with cancer (prostate, breast, colon, lung, etc.) or other diseases (diabetes, heart diseases, etc.) has made them new key players as biomarkers. Therefore, miRNA detection is of considerable significance in both disease diagnosis and in the study of miRNA function. Until these days, more than 1200 miRNAs have been identified. However, traditional methods developed for conventional DNA does not apply satisfactorily for miRNA, in particular due to the low expression level of these miRNA in biofluids, and because they are very short strands. Electrochemical biosensors can provide this sensitivity and also offer the advantages of mass fabrication, low-cost, and potential decentralized analysis, which has wide application for microRNAs sensing, with many promising results already reported. The present review summarizes some newly developed electrochemical miRNA detection methods.

The Prognostic Significance of miR-21 Expression among Surgically Resected Hepatocellular Carcinoma Patients: Evidence from a Meta-Analysis and Retrospective Cohort Study

Background

To date, microRNA-21 (miR-21) has been reported to be associated with the prognosis of hepatocellular carcinoma (HCC) in various studies, yet the results were inconsistent. The purpose of this two-part study, consisting of a retrospective cohort study and a meta-analysis, sets out to determine the prognostic role of miR-21 expression among HCC patients who underwent surgical resection. Methods. In this study, we first detected miR-21 expression in HCC patients by quantitative real-time PCR (qRT-PCR). Patients were divided into a high miR-21 expression group and a low miR-21 expression group according to the median level of miR-21 expression in tumor tissues. The survival outcomes of the two groups were analyzed by the Kaplan-Meier method with the log-rank test. Multivariate analysis of the prognostic factors was performed with the Cox regression model. Subsequently, eligible studies were obtained by searching on PubMed, Cochrane Library, and Web of Science, and a meta-analysis was performed to assess the prognostic role of miR-21 expression among HCC.

Results

The qRT-PCR analysis results of our cohort study showed miR-21 expression was significantly upregulated in HCC tissues when compared with adjacent nontumor tissues. Multivariate analysis suggested that miR-21 expression was an independent prognostic factor for overall survival (OS) (hazard ratio, HR = 2.361) and disease-free survival (DFS) (HR = 2.024) in HCC patients who underwent surgical resection. A total of 10 studies with 969 patients were enrolled in the meta-analysis, consisting of 9 studies from the database search and our cohort study. We observed that elevated miR-21 expression can predict poor OS (HR = 2.24, 95%CI = 1.73-2.91, P < 0.001) and DFS/recurrence-free survival (RFS) (HR = 2.44, 95%CI = 1.62-3.67, P < 0.001) in surgically resected HCC patients.

Conclusions

Our study demonstrated that miR-21 high expression among surgically resected HCC patients is a prognostic factor that indicated adverse survival.

Gold nanomaterials in the management of lung cancer

Lung cancer (LC) is one of the most deadly cancers worldwide, with very low survival rates, mainly due to poor management, which has barely changed in recent years. Nanomedicines, especially gold nanomaterials, with their unique and size-dependent properties offer a potential solution to many challenges in the field. The versatility afforded by the shape, size, charge and surface chemistry of gold nanostructures allows them to be adapted for many applications in the diagnosis, treatment and imaging of LC. In this review, a survey of the most recent advances in the field is presented with an emphasis on the optical properties of gold nanoscale materials and their use in cancer management. Gold nanoparticle toxicology has also been a focus of interest for many years but the studies have also sometimes arrived at contradictory conclusions. To enable extrapolation and facilitate the development of medicines based on gold nanomaterials, it must be assumed that each design will have its own unique characteristics that require evaluation before translation to the clinic. Advances in the understanding and recognition of the molecular signatures of LC have aided the development of personalised medicines. Tailoring the treatment to each case should, ideally increase the survival outcomes as well as reduce medical costs. This review seeks to present the potential of gold nanomaterials in LC management and to provide a unified view, which will be of interest to those in the field as well as researchers considering entering this highly important area of research.

Electrochemical Biosensors for Detection of MicroRNA as a Cancer Biomarker: Pros and Cons

Cancer is the second most fatal disease in the world and an early diagnosis is important for a successful treatment. Thus, it is necessary to develop fast, sensitive, simple, and inexpensive analytical tools for cancer biomarker detection. MicroRNA (miRNA) is an RNA cancer biomarker where the expression level in body fluid is strongly correlated to cancer. Various biosensors involving the detection of miRNA for cancer diagnosis were developed. The present review offers a comprehensive overview of the recent developments in electrochemical biosensor for miRNA cancer marker detection from 2015 to 2020. The review focuses on the approaches to direct miRNA detection based on the electrochemical signal. It includes a RedOx-labeled probe with different designs, RedOx DNA-intercalating agents, various kinds of RedOx catalysts used to produce a signal response, and finally a free RedOx indicator. Furthermore, the advantages and drawbacks of these approaches are highlighted.

Disposable 3D GNAs/AuNPs DNA-Circuit Strip for miRNAs Dynamic Quantification

Real-time quantitative monitoring of miRNAs plays an essential role in diagnosis and therapeutics. Herein, a DSN-coupled graphene nanoarray/gold nanoparticles (GNAs/AuNPs) carbon paper (CP) electrode for the dynamic, sensitive, and real-time analysis of miRNAs is reported. GNAs are vertically grown on the conductive CP by radio frequency plasma enhanced chemical vapor deposition, and AuNPs are electrodeposited on CP/GNAs to build a 3D ultrasensitive sensing interface with large specific surface area, good conductivity and biocompatibility. The dynamic quantitative monitoring of microRNA-21 (miR-21) is realized by cyclic voltammetry with a series of different concentrations within 16 min, and this 3D GNAs/AuNPs DNA-circuit strip shows good performance for the simultaneous detection of miR-21 and miR-155, and the detection limits are as low as 21.4 and 30.3 am, respectively. Moreover, comparable detection results are achieved for clinical samples between the proposed sensor and qRT-PCR, suggesting the reliability of the constructed sensor. This ultrasensitive sensing and disposable DNA-circuit strip with 3D structure can efficiently shorten the diffusion distance between reactive biomolecules and the sensing interface, enhance the hybridization of probes and improve the sensitivity of the biosensor, holding great promise for the rapid, quantitative and dynamic monitoring of multiple low concentrations of biomolecules in point-of-care clinical analysis.

A MoS2@Ti3C2Tx MXene hybrid-based electrochemical aptasensor (MEA) for sensitive and rapid detection of Thyroxine

In the present study, a MoS₂@Ti₃C₂T_x MXene hybrid-based electrochemical aptasensor (MEA) was introduced for sensitive and rapid quantification of Thyroxine (T4). T4 is a crucial hormone and plays a key role in various body functions. Therefore, there is high demand for an accurate, sensitive, and rapid method for the detection of T4. To construct the aptasensor, a nano-hybrid (NH) consisting of Ti₃C₂T_x MXene and MoS₂ nanosheets (NS) was synthesized, and applied to a carbon electrode surface, followed by the electroplating of gold nanostructures (GN). The smart combination of Ti₃C₂T_x MXene and MoS₂NS enhanced the physiochemical properties of the electrode surface, as well as provided a building block to form 3D GN. The 3D architecture of the GN offered a unique substrate to capture numerous T4 aptamer molecules, which consequently amplified the signal by nearly 6-fold. The MEA quantified thyroxine with a limit of detection (LOD) of 0.39 pg/mL over a dynamic range ((7.8 × 10^-1) to (7.8 × 10⁶)) pg/mL within 10 min. Moreover, the MEA successfully detected T4 in human serum samples. Lastly, the results obtained from the aptasensor were compared with those from the ELISA standard method. The comparative analysis showed good agreement between the two methods.

Nanostructuring Synergetic Base-Stacking Effect: An Enhanced Versatile Sandwich Sensor Enables Ultrasensitive Detection of MicroRNAs in Blood

MicroRNA (MiRNA)-based noninvasive diagnostics are hampered by the challenge in the quantification of circulating miRNAs using a general strategy. Here, we present a base-stacking effect-mediated ultrasensitive electrochemical miRNA sensor (BSee-miR) with a universal sandwich configuration. In the BSee-miR, a short DNA probe (10 nucleotides) self-assembled on a gold electrode surface could effectively capture the target miRNA synergizing with another sequence based on coaxial sandwich base-stacking, which rivals the fully complementary strength. Importantly, such a sandwich structure is flexible to incorporate signal amplification strategies (e.g., biotin-avidin) that are usually difficult to achieve in short sequence detection. Using this design, the BSee-miR achieves a broad dynamic range with a detection limit down to 7.5 fM. Furthermore, we found a high-curvature nanostructuring synergetic base-stacking effect that could improve the sensitivity of the BSee-miR by two orders of magnitude (79.3 aM). Our BSee-miR also has a single-base resolution to discriminate the highly homologous miRNAs. More importantly, this approach is universal and has been used to probe target miRNAs varying in sequences and secondary structures. Our ultrasensitive sensor could detect miRNA in cell lysates and human blood and distinguish cancer patients from normal individuals, promising a versatile tool to measure clinically relevant miRNAs for tumor diagnostics.

Nanobioconjugates for Signal Amplification in Electrochemical Biosensing

Nanobioconjugates are hybrid materials that result from the coalescence of biomolecules and nanomaterials. They have emerged as a strategy to amplify the signal response in the biosensor field with the potential to enhance the sensitivity and detection limits of analytical assays. This critical review collects a myriad of strategies for the development of nanobioconjugates based on the conjugation of proteins, antibodies, carbohydrates, and DNA/RNA with noble metals, quantum dots, carbon- and magnetic-based nanomaterials, polymers, and complexes. It first discusses nanobioconjugates assembly and characterization to focus on the strategies to amplify a biorecognition event in biosensing, including molecular-, enzymatic-, and electroactive complex-based approaches. It provides some examples, current challenges, and future perspectives of nanobioconjugates for the amplification of signals in electrochemical biosensing.

Seed-mediated Electrochemically Developed Au Nanostructures with Boosted Sensing Properties: An Implication for Non-enzymatic Glucose Detection

A new approach has been developed to improve sensing performances of electrochemically grown Au nanostructures (AuNSs) based on the pre-seeding of the electrode. The pre-seeding modification is simply carried out by vacuum thermal deposition of 5 nm thin film of Au on the substrate followed by thermal annealing at 500 °C. The electrochemical growth of AuNSs on the pre-seeded substrates leads to impressive electrochemical responses of the electrode owing to the seeding modification. The dependence of the morphology and the electrochemical properties of the AuNSs on various deposition potentials and times have been investigated. For the positive potentials, the pre-seeding leads to the growth of porous and hole-possess networks of AuNSs on the surface. For the negative potentials, AuNSs with carved stone ball shapes are produced. The superior electrode was achieved from AuNSs developed at 0.1 V for 900 s with pre-seeding modification. The sensing properties of the superior electrode toward glucose detection show a high sensitivity of 184.9 µA mM⁻¹ cm⁻², with a remarkable detection limit of 0.32 µM and a wide range of linearity. The excellent selectivity and reproducibility of the sensors propose the current approach as a large-scale production route for non-enzymatic glucose detection.

Electrochemical detection of β-lactoglobulin based on a highly selective DNA aptamer and flower-like Au@BiVO4 microspheres

Beta-lactoglobulin is a natural milk protein and the main cause of infant milk allergy. In this work, a sensitive, selective and inexpensive electrochemical biosensor for the detection of β-lactoglobulin was developed. In this sensor, a DNA aptamer was used instead of an expensive antibody as the recognition group highly selective for β-lactoglobulin. The flower-like BiVO₄ microspheres were firstly found to have peroxidase mimic catalytic activity and used to amplify the electrochemical signal. The aptamer can bind β-lactoglobulin and fall off from the working electrode, after which the DNA2/Au/BiVO₄ probe can be fixed to the DNA1/AuNPs/ITO working electrode by the hybridization of DNA2 with DNA1. Therefore, a higher concentration of β-lactoglobulin leads to increased fabrication of the DNA2/Au/BiVO₄ probe on the surface of the working electrode, and thereby increases the electrochemical signal. This electrochemical biosensor exhibited a wide detection range from 0.01 to 1000 ng mL^-1, with a limit of detection (LOD) of 0.007 ng mL^-1, which indicates a good potential application in the field of food analysis.

Hierarchically Ordered Silicon Metastructures from Improved Self-Assembly-Based Nanosphere Lithography

We developed an improved self-assembly method to obtain a large-area, high-quality templated monolayer mask using the polystyrene spheres. On the basis of the templated mask, hierarchically ordered Si metastructures with different nanosteps are fabricated using cyclic inductively coupled plasma etching technique. By evaporating a thin gold capping layer on these Si metastructures, their optical properties are comparatively studied using the surface-enhanced Raman scattering spectroscopy. Our proposed technique is highly promising for fabricating a variety of periodic three-dimensional hierarchically ordered metastructures, which could be further utilized for applications in SERS-based biosensors, optical absorbers, metamaterial/metasurface devices, etc.

Synergy of Peptide-Nucleic Acid and Spherical Nucleic Acid Enabled Quantitative and Specific Detection of Tumor Exosomal MicroRNA

Exosomal microRNAs are essential in intercellular communications and disease progression, yet it remains challenging to quantify the expression level due to their small size and low abundance in blood. Here, we report a "sandwich" electrochemical exosomal microRNA sensor (SEEmiR) to detect target microRNA with high sensitivity and specificity. In SEEmiR, neutrally charged peptide nucleic acid (PNA) enables kinetically favorable hybridization with the microRNA target relative to negatively charged DNA, particularly in a short sequence (10 nt). More importantly, this property allows PNA to cooperate with a spherical nucleic acid (SNA) nanoprobe that heavily loads with oligonucleotide-adsorbed electroactive tags to enhance detection sensitivity and specificity. Such a PNA-microRNA-SNA sandwich construct is able to minimize the background noise via PNA, thereby maximizing the SNA-mediated signal amplification in electrostatic adsorption-based SEEmiR. The synergy between PNA and SNA makes the SEEmiR sensor able to achieve a broad dynamic range (from 100 aM to 1 nM) with a detection limit down to 49 aM (2 orders of magnitude lower than that without SNA) and capable of distinguishing a single-base mismatch. This ultrasensitive sensor provides label-free and enzyme-independent microRNA detection in cell lysates, unpurified tumor exosomal lysates, cancer patients' blood, and accurately differentiates the patients with breast cancer from the healthy ones, suggesting its potential as a promising tool in cancer diagnostics.