Few-Layer MoS2 Photodetector Arrays for Ultrasensitive On-Chip Enzymatic Colorimetric Analysis

Alkaline liquid-derived NaxTi11.5MoVOx/C-40 material with controlled electron transfer rate for sensitive electrochemical detection of dopamine

The neurotransmitter dopamine (DA) is associated with many physiological and pathological processes, so the importance of low detection limits and high sensitivity analysis cannot be overstated, especially for early disease detection. Here, 2 M NaOH aqueous solution is used to precipitate metal ions in an ethanol solution containing carbon black (CB), and then nanocomposite catalysts (NaxTi11.5MoVOx/C-40 (40 denoted as 40 mg CB)) were obtained by calcining the precipitation. When used for DA detection, NaxVOx acts as the main active site for electrochemical oxidation of DA and NaxTi11.5MoOx plays a role in facilitating the binding of DA to the active site and stabilizing the active site. The NaxTi11.5MoVOx/C-40 electrochemical biosensor has a limit of detection (LOD) of 0.003 μM with a linear range of 0.005-51.665 μM for DA. This sensor can be used to sensitively identify the concentration of DA in human blood and urine. Catalysts containing varying amounts of CB exhibit diverse electron transfer rates, and surprisingly, we found that the appropriate electron transfer rate is optimal for the detection of low concentrations of DA. Because the performance of the electrochemical biosensors is affected by both the activity of the catalysts and the accuracy of the electrochemical testing instrumentation. To better explain this phenomenon, we propose the concept of resolution (Rn) and present the formula to derive it, offering a new approach to evaluating the performance of electrochemical biosensors.

Saliva Analysis Based on Microfluidics: Focusing the Wide Spectrum of Target Analyte

Saliva is one of the most critical human body fluids that can reflect the state of the human body. The detection of saliva is of great significance for disease diagnosis and health monitoring. Microfluidics, characterized by microscale size and high integration, is an ideal platform for the development of rapid and low-cost disease diagnostic techniques and devices. Microfluidic-based saliva testing methods have aroused considerable interest due to the increasing need for noninvasive testing and frequent or long-term testing. This review briefly described the significance of saliva analysis and generally classified the targets in saliva detection into pathogenic microorganisms, inorganic substances, and organic substances. By using this classification as a benchmark, the state-of-the-art research results on microfluidic detection of various substances in saliva were summarized. This work also put forward the challenges and future development directions of microfluidic detection methods for saliva.

Emerging open-channel droplet arrays for biosensing

Open-channel droplet arrays have attracted much attention in the fields of biochemical analysis, biofluid monitoring, biomarker recognition and cell interactions, as they have advantages with regard to miniaturization, parallelization, high-throughput, simplicity and accessibility. Such droplet arrays not only improve the sensitivity and accuracy of a biosensor, but also do not require sophisticated equipment or tedious processes, showing great potential in next-generation miniaturized sensing platforms. This review summarizes typical examples of open-channel microdroplet arrays and focuses on diversified biosensing integrated with multiple signal-output approaches (fluorescence, colorimetric, surface-enhanced Raman scattering (SERS), electrochemical, etc.). The limitations and development prospects of open-channel droplet arrays in biosensing are also discussed with regard to the increasing demand for biosensors.

Highly Active CoRh Graphitic Nanozyme for Colorimetric Sensing in Real Samples

Rh-based nanozymes show high catalytic efficiency, specific surface area, good stability, and unique physicochemical properties, while magnetic nanozymes facilitate the magnetic separation of detection samples under an external magnetic field for improved sensitivity. However, magnetic Rh nanozymes, especially those with excellent stability, have not been reported. Herein, we apply the chemical vapor deposition (CVD) method to prepare a CoRh graphitic nanozyme (termed as CoRh@G nanozyme), which structurally consists of CoRh nanoalloy encapsulated by a few layers of graphene for sensitive colorimetric sensing applications. The proposed CoRh@G nanozyme has superior peroxidase (POD)-like activity, and it shows higher affinity of the CoRh@G nanozyme than horseradish peroxidase (HRP) toward 3,3',5,5'-tetramethylbenzydine (TMB) oxidation. In addition, the CoRh@G nanozyme shows high durability and superior recyclability owing to its protective graphitic shell. The outstanding merits of the CoRh@G nanozyme allow its use for quantitative colorimetric detection of dopamine (DA) and ascorbic acid (AA), showing high sensitivity and good selectivity. Moreover, it shows satisfactory performance for AA detection in commercial beverages and energy drinks. The proposed CoRh@G nanozyme-based colorimetric sensing platform shows great promise in point-of-care (POC) visual monitoring.

Emerging Trends in 2D TMDs Photodetectors and Piezo-Phototronic Devices

The piezo-phototronic effect shows promise with regards to improving the performance of 2D semiconductor-based flexible optoelectronics, which will potentially open up new opportunities in the electronics field. Mechanical exfoliation and chemical vapor deposition (CVD) influence the piezo-phototronic effect on a transparent, ultrasensitive, and flexible van der Waals (vdW) heterostructure, which allows the use of intrinsic semiconductors, such as 2D transition metal dichalcogenides (TMD). The latest and most promising 2D TMD-based photodetectors and piezo-phototronic devices are discussed in this review article. As a result, it is possible to make flexible piezo-phototronic photodetectors, self-powered sensors, and higher strain tolerance wearable and implantable electronics for health monitoring and generation of piezoelectricity using just a single semiconductor or vdW heterostructures of various nanomaterials. A comparison is also made between the functionality and distinctive properties of 2D flexible electronic devices with a range of applications made from 2D TMDs materials. The current state of the research about 2D TMDs can be applied in a variety of ways in order to aid in the development of new types of nanoscale optoelectronic devices. Last, it summarizes the problems that are currently being faced, along with potential solutions and future prospects.

Nanopatterning Technologies of 2D Materials for Integrated Electronic and Optoelectronic Devices

With the reduction of feature size and increase of integration density, traditional 3D semiconductors are unable to meet the future requirements of chip integration. The current semiconductor fabrication technologies are approaching their physical limits based on Moore's law. 2D materials such as graphene, transitional metal dichalcogenides, etc., are of great promise for future memory, logic, and photonic devices due to their unique and excellent properties. To prompt 2D materials and devices from the laboratory research stage to the industrial integrated circuit-level, it is necessary to develop advanced nanopatterning methods to obtain high-quality, wafer-scale, and patterned 2D products. Herein, the recent development of nanopatterning technologies, particularly toward realizing large-scale practical application of 2D materials is reviewed. Based on the technological progress, the unique requirement and advances of the 2D integration process for logic, memory, and optoelectronic devices are further summarized. Finally, the opportunities and challenges of nanopatterning technologies of 2D materials for future integrated chip devices are prospected.

Nanomaterials-assisted metabolic analysis toward in vitro diagnostics

In vitro diagnostics (IVD) has played an indispensable role in healthcare system by providing necessary information to indicate disease condition and guide therapeutic decision. Metabolic analysis can be the primary choice to facilitate the IVD since it characterizes the downstream metabolites and offers real-time feedback of the human body. Nanomaterials with well-designed composition and nanostructure have been developed for the construction of high-performance detection platforms toward metabolic analysis. Herein, we summarize the recent progress of nanomaterials-assisted metabolic analysis and the related applications in IVD. We first introduce the important role that nanomaterials play in metabolic analysis when coupled with different detection platforms, including electrochemical sensors, optical spectrometry, and mass spectrometry. We further highlight the nanomaterials-assisted metabolic analysis toward IVD applications, from the perspectives of both the targeted biomarker quantitation and untargeted fingerprint extraction. This review provides fundamental insights into the function of nanomaterials in metabolic analysis, thus facilitating the design of next-generation diagnostic devices in clinical practice.

Embedding Proteins within Spatially Controlled Hierarchical Nanoarchitectures for Ultrasensitive Immunoassay

Modulating the precise self-assembly of functional biomacromolecules is a critical challenge in biotechnology. Herein, functional biomacromolecule-assembled hierarchical hybrid nanoarchitectures in a spatially controlled fashion are synthesized, achieving the biorecognition behavior and signal amplification in the immunoassay simultaneously. Biomacromolecules with sequential assembly on the scaffold through the biomineralization process show significantly enhanced stability, bioactivity, and utilization efficiency, allowing tuning of their functions by modifying their size and composition. The hierarchically hybrid nanoarchitectures show great potential in construction of ultrasensitive immunoassay platforms, achieving a three order-of-magnitude increase in sensitivity. Notably, the well-designed HRP@Ab₂ nanoarchitectures allow for optical immunoassays with a detection range from picogram mL^-1 to microgram mL^-1 on demand, providing great promise for quantitative analysis of both low-abundance and high-residue targets for biomedical applications.