Atomically thin transition metal dichalcogenides have emerged as promising candidates for sensitive photodetection. Here, we report a photoconductivity study of biased mono- and bilayer molybdenum disulfide field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photogain. The photovoltaic effect is described as a shift in transistor threshold voltage due to charge transfer from the channel to nearby molecules, including SiO2 surface-bound water. The photoconductive effect is attributed to the trapping of carriers in band tail states in the molybdenum disulfide itself. A simple model is presented that reproduces our experimental observations, such as the dependence on incident optical power and gate voltage. Our findings offer design and engineering strategies for atomically thin molybdenum disulfide photodetectors, and we anticipate that the results are generalizable to other transition metal dichalcogenides as well.

Mechanisms of photoconductivity in atomically thin MoS2

Synthesis of Wafer-Scale Graphene with Chemical Vapor Deposition for Electronic Device Applications

A CRISPR/Cas13a-powered catalytic electrochemical biosensor for successive and highly sensitive RNA diagnostics.

Graphene oxide-graphene Van der Waals heterostructure transistor biosensor for SARS-CoV-2 protein detection

(Mi)RNAs are important biomarkers for cancers diagnosis and pandemic diseases, which require fast, ultrasensitive, and economical detection strategies to quantitatively detect exact (mi)RNAs expression levels. The novel coronavirus disease (SARS-CoV-2) has been breaking out globally, and RNA detection is the most effective way to identify the SARS-CoV-2 virus. Here, we developed an ultrasensitive poly-l-lysine (PLL)-functionalized graphene field-effect transistor (PGFET) biosensor for breast cancer miRNAs and viral RNA detection. PLL is functionalized on the channel surface of GFET to immobilize DNA probes by the electrostatic force. The results show that PGFET biosensors can achieve a (mi)RNA detection range of five orders with a detection limit of 1 fM and an entire detection time within 20 min using 2 μL of human serum and throat swab samples, which exhibits more than 113% enhancement in terms of sensitivity compared to that of GFET biosensors. The performance enhancement mechanisms of PGFET biosensors were comprehensively studied based on an electrical biosensor theoretical model and experimental results. In addition, the PGFET biosensor was applied for the breast cancer miRNA detection in actual serum samples and SARS-CoV-2 RNA detection in throat swab samples, providing a promising approach for rapid cancer diagnosis and virus screening.

https://pubs.acs.org/doi/pdf/10.1021/acs.analchem.1c03786

Poly-l-Lysine-Modified Graphene Field-Effect Transistor Biosensors for Ultrasensitive Breast Cancer miRNAs and SARS-CoV-2 RNA Detection

Non-invasive early diagnosis is of great significance in disease pathologic development and subsequent medical treatments, and microRNA (miRNA) detection has attracted critical attention in early cancer screening and diagnosis. High-throughput, sensitive, economic, and fast miRNA sensing platforms are necessary to realize the low-concentration miRNA detection in clinical diagnosis and biological studies. Here, we developed an attomolar-level ultrasensitive, rapid, and multiple-miRNA simultaneous detection platform enabled by nanomaterial locally assembled microfluidic biochips. This platform presents a large linear detection regime of 1 aM-10 nM, an ultralow detection limit of 0.146 aM with no amplification, a short detection time of 35 min with multiplex miRNA sensing capability, and a small sample volume consumption of 2 μL. The detection results of five miRNAs in real samples from breast cancer patients and healthy humans indicate its excellent capacity for practical applications in early cancer diagnosis. The proposed ultrasensitive, rapid, and multiple-miRNA detection microfluidic biochip platform is a universal miRNA detection approach and an important and valuable tool in early cancer screening and diagnosis as well as biological studies.

Attomolar-Level Ultrasensitive and Multiplex microRNA Detection Enabled by a Nanomaterial Locally Assembled Microfluidic Biochip for Cancer Diagnosis.

It is urgent to establish a fast, convenient, accurate, and low-cost miRNA quantitative detection platform, which is important in disease development and the early diagnosis of cancer. Here, we propose a miRNA-specific detection microfluidic platform in which a self-assembled Poly-L-Lysine (PLL) substrate is integrated with microfluidic chips and conduct multiple detection of miRNAs from multiple samples at the same time based on three-segment hybridization. PLL is first self-assembled onto a clean glass slide and then integrated with a high-throughput micro-printing microfluidic chip to locally mobilize DNA probes. A sample-loading microfluidic chip is designed to realize multiple detection of multiple samples at the same time. A three-segment hybridization system is used to detect miRNAs in which the capture probe is complementary to one end of the target miRNA and the detection probe with fluorescence is complementary to the other end of the target miRNA. First, capture probes are mobilized on the chip and detection probes with fluorescence are hybridized with the target miRNA. Second, a miRNA-detection probe hybridizer is reacted with the capture probes immobilized on the chip. Finally, excessive detection probes are cleaned and the fluorescence intensity of the capture probe–miRNA–detection probe hybridizer on the chip is detected by using a laser scanner. Four significant breast cancer biomarker miRNAs are selected for simultaneous detection, and the detection limit is 1 pM with a detection time of 30 min. This microfluidic platform shows sensitive multiple detection of miRNAs in multiple samples and is promising for the early diagnosis of breast cancer.

Chu Yujin

Papers

Attomolar-Level Ultrasensitive and Multiplex microRNA Detection Enabled by a Nanomaterial Locally Assembled Microfluidic Biochip for Cancer Diagnosis.

Microfluidic chip for multiple detection of miRNA biomarkers in breast cancer based on three-segment hybridization

Large area uniform PtSx synthesis on sapphire substrate for performance improved photodetectors