Dual-Target Electrochemical Biosensing Based on DNA Structural Switching on Gold Nanoparticle-Decorated MoS2 Nanosheets

Electrochemical DNA sensors based on spatially distributed redox mediators: challenges and promises

DNA and aptasensors are widely used for fast and reliable detection of disease biomarkers, pharmaceuticals, toxins, metabolites and other species necessary for biomedical diagnostics. In the overview, the concept of spatially distributed redox mediators is considered with particular emphasis to the signal generation and biospecific layer assembling. The application of non-conductive polymers bearing redox labels, supramolecular carriers with attached DNA aptamers and redox active dyes and E-sensor concept are considered as examples of the approach announced.

Real-Time Continuous Identification of Greenhouse Plant Pathogens Based on Recyclable Microfluidic Bioassay System

The development of a real-time continuous analytical platform for the pathogen detection is of great scientific importance for achieving better disease control and prevention. In this work, we report a rapid and recyclable microfluidic bioassay system constructed from oligonucleotide arrays for selective and sensitive continuous identification of DNA targets of fungal pathogens. We employ the thermal denaturation method to effectively regenerate the oligonucleotide arrays for multiple sample detection, which could considerably reduce the screening effort and costs. The combination of thermal denaturation and laser-induced fluorescence detection technique enables real-time continuous identification of multiple samples (<10 min per sample). As a proof of concept, we have demonstrated that two DNA targets of fungal pathogens (Botrytis cinerea and Didymella bryoniae) can be sequentially analyzed using our rapid microfluidic bioassay system, which provides a new paradigm in the design of microfluidic bioassay system and will be valuable for chemical and biomedical analysis.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Two-Dimensional 1T-Phase Transition Metal Dichalcogenides as Nanocarriers To Enhance and Stabilize Enzyme Activity for Electrochemical Pesticide Detection

Single or few layers lithium-exfoliated transition metal dichalcogenides (TMDs) are found to exist predominantly in the conducting metallic 1T-polymorph, which makes it desirable for numerous applications due to its large surface area, good electrical conductivity, and enhanced electrocatalytic capabilities. We demonstrated the use of tert-butyllithium exfoliated TMDs (MoS₂, MoSe₂, WS₂, WSe₂) as a platform for the indirect electrochemical detection of an organophosphate pesticide, fenitrothion, via enzymatic inhibition pathway. All four reported materials enhanced the response of the enzymatic biosensor in comparison to the corresponding biosensor in the absence of TMDs. 1T-Phase WS₂ outperforms all other TMD materials, and we proved that it serves as an excellent transducer for enhancing electron transfer in a robust model enzyme-based inhibition assay system using cross-linking immobilization with glutaraldehyde. The reported system showed a broad fenitrothion concentration range (1-1000 nM) with an excellent linearity (r = 0.987). Moreover, the system displayed high sensitivity with low limit of detection (2.86 nM) obtained, which far exceeds the required limit set by Food and Agriculture Organisation (FAO) of the United Nations (UN). The feasibility of the proposed system in real samples was demonstrated in apple juice samples with good recoveries of 80.2% and 80.3% obtained at 10 and 1000 nM fenitrothion, respectively.

Biotunable Nanoplasmonic Filter on Few-Layer MoS2 for Rapid and Highly Sensitive Cytokine Optoelectronic Immunosensing

Monitoring of the time-varying immune status of a diseased host often requires rapid and sensitive detection of cytokines. Metallic nanoparticle-based localized surface plasmon resonance (LSPR) biosensors hold promise to meet this clinical need by permitting label-free detection of target biomolecules. These biosensors, however, continue to suffer from relatively low sensitivity as compared to conventional immunoassay methods that involve labeling processes. Their response speeds also need to be further improved to enable rapid cytokine quantification for critical care in a timely manner. In this paper, we report an immunobiosensing device integrating a biotunable nanoplasmonic optical filter and a highly sensitive few-layer molybdenum disulfide (MoS₂) photoconductive component, which can serve as a generic device platform to meet the need of rapid cytokine detection with high sensitivity. The nanoplasmonic filter consists of anticytokine antibody-conjugated gold nanoparticles on a SiO₂ thin layer that is placed 170 μm above a few-layer MoS₂ photoconductive flake device. The principle of the biosensor operation is based on tuning the delivery of incident light to the few-layer MoS₂ photoconductive flake thorough the nanoplasmonic filter by means of biomolecular surface binding-induced LSPR shifts. The tuning is dependent on cytokine concentration on the nanoplasmonic filter and optoelectronically detected by the few-layer MoS₂ device. Using the developed optoelectronic biosensor, we have demonstrated label-free detection of IL-1β, a pro-inflammatory cytokine, with a detection limit as low as 250 fg/mL (14 fM), a large dynamic range of 10⁶, and a short assay time of 10 min. The presented biosensing approach could be further developed and generalized for point-of-care diagnosis, wearable bio/chemical sensing, and environmental monitoring.

Integrated signal probe based aptasensor for dual-analyte detection

For the multi-analyte detection, although the sensitivity has commonly met the practical requirements, the reliability, reproducibility and stability need to be further improved. In this work, two different aptamer probes labeled with redox tags were used as signal probe1 (sP1) and signal probe2 (sP2), which were integrated into one unity DNA architecture to develop the integrated signal probe (ISP). Comparing with the conventional independent signal probes for the simultaneous multi-analyte detection, the proposed ISP was more reproducible and accurate. This can be due to that ISP in one DNA structure can ensure the completely same modification condition and an equal stoichiometric ratio between sP1 and sP2, and furthermore the cross interference between sP1 and sP2 can be successfully prevented by regulating the complementary position of sP1 and sP2. The ISP-based assay system would be a great progress for the dual-analyte detection. Combining with gold nanoparticles (AuNPs) signal amplification, the ISP/AuNPs-based aptasensor for the sensitive dual-analyte detection was explored. Based on DNA structural switching induced by targets binding to aptamer, the simultaneous dual-analyte detection was simply achieved by monitoring the electrochemical responses of methylene blue (MB) and ferrocene (Fc) This proposed detection system possesses such advantages as simplicity in design, easy operation, good reproducibility and accuracy, high sensitivity and selectivity, which indicates the excellent application of this aptasensor in the field of clinical diagnosis or other molecular sensors.

Facile Synthesis of a MoS2-Prussian Blue Nanocube Nanohybrid-Based Electrochemical Sensing Platform for Hydrogen Peroxide and Carcinoembryonic Antigen Detection

Herein, an electrochemical detection platform was designed based on a Prussian blue nanocube-decorated molybdenum disulfide (MoS₂-PBNCs) nanocomposite. Shape-controlled and high-dispersion PBNCs were supported on the MoS₂ nanosheet surface, which would be simply controlled by varying the experimental conditions. Expectedly, such obtained MoS₂-based nanocomposites possessed excellent electrocatalytic ability, which could be employed to construct an electrochemical sensor for nonenzymatic hydrogen peroxide (H₂O₂) detection. More interestingly, MoS₂-PBNCs nanocomposites could be utilized to construct a sensor for label-free detection of carcinoembryonic antigen (CEA). The electrochemical response of the MoS₂-based immunosensor was linear with the CEA concentration ranging from 0.005 to 10 ng mL^-1. Moreover, the detection limit was calculated to be 0.54 pg mL^-1. The acceptable selectivity and high stability made such immunosensors detect CEA in human serum with satisfactory results. All data indicated that this MoS₂-PBNCs nanocomposite may be a promising electrochemical sensing platform for the detection of chemical and biological molecules.

Dual-mode electrochemical analysis of microRNA-21 using gold nanoparticle-decorated MoS2 nanosheet

The detection of microRNA plays an important role in early cancer diagnosis. Herein, a dual-mode electronic biosensor was developed for microRNA-21 (miRNA-21) detection based on gold nanoparticle-decorated MoS₂ nanosheet (AuNPs@MoS₂). A classical DNA "sandwich" structure was employed to construct MoS₂-based electrochemical sensor, including capture DNA, target miRNA-21 and DNA-modified nanoprobe. [Fe(CN)₆]^3-/4- and [Ru(NH₃)₆]³⁺ were selected as electrochemical indicators to monitor the preparation process and evaluate the performance of MoS₂-based electrochemical biosensor by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV), respectively. Such MoS₂-based biosensor exhibited excellent performance for miRNA-21 detection in the range from 10 fM to 1nM with detection limit of 0.78fM and 0.45fM for DPV and EIS technique, respectively. Furthermore, the proposed MoS₂-based biosensor displayed high selectivity and stability, which could be used to determine miRNA-21 in human serum samples with satisfactory results. All data suggested that such MoS₂-based nanocomposite may be a potential candidate for biosensing ranging from nucleic acid to protein detection.

Recent Advances in Synthesis and Biomedical Applications of Two-Dimensional Transition Metal Dichalcogenide Nanosheets

During recent decades, a giant leap in the development of nanotechnology has been witnessed. Numerous nanomaterials with different dimensions and unprecedented features have been developed and provided unimaginably wide scope to solve the challenging problems in biomedicine, such as cancer diagnosis and therapy. Recently, two-dimensional (2D) transition metal dichalcogenide (TMDC) nanosheets (NSs), including MoS₂ , WS₂ , and etc., have emerged as novel inorganic graphene analogues and attracted tremendous attention due to their unique structures and distinctive properties, and opened up great opportunities for biomedical applications, including ultrasensitive biosensing, biological imaging, drug delivery, cancer therapy, and antibacterial treatment. A comprehensive overview of different synthetic methods of ultrathin 2D TMDC NSs and their state-of-the-art biomedical applications, especially those that have appeared in the past few years, is presented. At the end of this review, the future opportunities and challenges for 2D TMDC NSs in biomedicine are also discussed.

A sensitive, uniform, reproducible and stable SERS substrate has been presented based on MoS2@Ag nanoparticles@pyramidal silicon

By combine the Ag nanoparticles, pyramidal silicon and molybdenum disulfide, the MoS₂@AgNPs@PSi substrate shows high performance in terms of sensitivity, uniformity, reproducibility and stability.

MoS2-DNA and MoS2 based sensors

MoS₂, a family member of transition-metal dichalcogenides, has shown highly attractive superiority for detection arising from its unique physical and chemical properties.

Hybridization chain reaction-based colorimetric aptasensor of adenosine 5'-triphosphate on unmodified gold nanoparticles and two label-free hairpin probes

This work designs a new label-free aptasensor for the colorimetric determination of small molecules (adenosine 5'-triphosphate, ATP) by using visible gold nanoparticles as the signal-generation tags, based on target-triggered hybridization chain reaction (HCR) between two hairpin DNA probes. The assay is carried out referring to the change in the color/absorbance by salt-induced aggregation of gold nanoparticles after the interaction with hairpins, gold nanoparticles and ATP. To construct such an assay system, two hairpin DNA probes with a short single-stranded DNA at the sticky end are utilized for interaction with gold nanoparticles. In the absence of target ATP, the hairpin DNA probes can prevent gold nanoparticles from the salt-induced aggregation through the interaction of the single-stranded DNA at the sticky end with gold nanoparticles. Upon target ATP introduction, the aptamer-based hairpin probe is opened to expose a new sticky end for the strand-displacement reaction with another complementary hairpin, thus resulting in the decreasing single-stranded DNA because of the consumption of hairpins. In this case, gold nanoparticles are uncovered owing to the formation of double-stranded DNA, which causes their aggregation upon addition of the salt, thereby leading to the change in the red-to-blue color. Under the optimal conditions, the HCR-based colorimetric assay presents good visible color or absorbance responses for the determination of target ATP at a concentration as low as 1.0nM. Importantly, the methodology can be further extended to quantitatively or qualitatively monitor other small molecules or biotoxins by changing the sequence of the corresponding aptamer.