Saxitoxin (STX) is one of the most important marine toxins which affects the safety of domestic water. Rapid, sensitive and selective recognition of STX is crucial in environment monitoring. Here, we demonstrate a facile and ultrasensitive colorimetric sensor based on gold nanoparticles (Au NPs) and aptamer (Au NPs-aptamer biosensor) for specific and quantitative detection of STX. The aptamer reacts specifically with STX, resulting in the aggregation of Au NPs and the color change of the Au NP solution. The lowest detection concentration of the colorimetric sensor is 10 fM (3 fg mL⁻¹), and a good linear relationship (R² = 0.9852) between the absorbance ratio and STX concentrations (10 fM to 0.1 μM) indicates that our Au NPs-aptamer biosensor can be used for quantitative sensing of STX. The detection time of STX is 30 minutes, and the sensor is successfully applied in the specific detection of STX in seawater. The Au NP-aptamer biosensor shows great potential in practical applications to monitor environmental pollution, marine aquaculture pollution, and seafood safety.

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.

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, rapid and portable double-layer microfluidic biochip for the simultaneous quantitative detection of six species of algae. Specific DNA probes based on the 18S ribosomal DNA (18S rDNA) gene fragments of HABs were designed and labeled with the fluorescent molecule cyanine-3 (Cy3). The biochip had multiple graphene oxide (GO) nanosheets-based reaction units, in which GO nanosheets were applied to transfer target DNA to the fluorescence signal through a photoluminescence detection system. The entire detection process of multiple algae was completed within 45 min with the linear range of fluorescence recovery of 0.1 fM–100 nM, and the detection limit reached 108 aM. The proposed approach has a simple detection process and high detection performance and is feasible to conduct accurate detection with matched portable detection equipment. It will have promising applications in marine natural disaster monitoring and environmental care.

A rGO-based biosensor can detect SARS-CoV-2 RNA within 35 minutes with a LOD of 0.684 pM without any amplification.