Rapid and Sensitive Detection of miRNA Based on AC Electrokinetic Capacitive Sensing for Point-of-Care Applications.

A sensitive and efficient method for microRNAs (miRNAs) detection is strongly desired by clinicians and, in recent years, the search for such a method has drawn much attention. There has been significant interest in using miRNA as biomarkers for multiple diseases and conditions in clinical diagnostics. Presently, most miRNA detection methods suffer from drawbacks, e.g., low sensitivity, long assay time, expensive equipment, trained personnel, or unsuitability for point-of-care. New methodologies are needed to overcome these limitations to allow rapid, sensitive, low-cost, easy-to-use, and portable methods for miRNA detection at the point of care. In this work, to overcome these shortcomings, we integrated capacitive sensing and alternating current electrokinetic effects to detect specific miRNA-16b molecules, as a model, with the limit of detection reaching 1.0 femto molar (fM) levels. The specificity of the sensor was verified by testing miRNA-25, which has the same length as miRNA-16b. The sensor we developed demonstrated significant improvements in sensitivity, response time and cost over other miRNA detection methods, and has application potential at point-of-care.

Capacitive DNA sensor for rapid and sensitive detection of whole genome human herpesvirus-1 dsDNA in serum.

This work presents a rapid, highly sensitive, low-cost, and specific capacitive DNA sensor for detection of whole genome human herpesvirus-1 DNA. This sensor is capable of direct DNA detection with a response time of 30 s, and it can be used to test standard buffer or serum samples. The sensing approach for DNA detection is based on alternating current (AC) electrokinetics. By applying an inhomogeneous AC electric field on sensor electrodes, positive dielectrophoresis is induced to accelerate DNA hybridization. The same applied AC signal also directly measures the hybridization of target with the probe on the sensor surface. Experiments are conducted to optimize the AC signal, as well as the buffers for probe immobilization and target DNA hybridization. The assay is highly sensitive and specific, with no response to human herpesvirus-2 DNA at 5 ng/mL and a LOD of 1.0 pg/mL (6.5 copies/µL or 10.7 aM) in standard buffer. When testing the double stranded (ds) DNA spiked in human serum samples, the sensor yields a LOD of 20.0 pg/mL (129.5 copies/µL or 0.21 femtomolar (fM)) in neat serum. In this work, the target is whole genome dsDNA, consequently the test can be performed without the use of enzyme or amplification, which considerably simplifies the sensor operation and is highly suitable for point of care disease diagnosis.

Highly sensitive and specific on-site detection of serum cocaine by a low cost aptasensor.

Cocaine is one of the most used illegal recreational drugs. Developing an on-site test for cocaine use detection has been a focus of research effort, since it is essential to the control and legal action against drug abuse. Currently most of cocaine detection methods are time-consuming and require special or expensive equipment, and the detection often suffers from high cross-reactivity with cocaine metabolites and relative low sensitivity with the best limit of detection reported at sub nanomolar (nM) level. In this work, an aptasensor has been developed using capacitive monitoring of sensor surface incorporating alternating current electrokinetics effects to speed up molecular transport and minimize matrix effects. The aptasensor is rapid, low cost, highly sensitive and specific as well as simple-to-use for the detection of cocaine from serum. The assay has a sample-to-result time of 30 s, a limit of detection of 7.8 fM, and a linear response for cocaine ranging from 14.5fM to 14.5pM in standard buffer, which are great improvements from other reported cocaine sensors. Special buffer is used for serum cocaine detection, and a limit of detection of 13.4 fM is experimentally demonstrated for cocaine spiked in human serum (equivalent to 1.34pM cocaine in neat serum). The specificity of the biosensor is also demonstrated with structurally similar chemicals, ecgonine ethyl ester and methylecgonidine. This biosensor shows high promise in detection of low levels of cocaine from complex matrices.

Simple, Fast And Highly Sensitive Detection Of Gram-Negative Bacteria By A Novel Electrical Biosensor.

This work presents a rapid, low-cost, highly sensitive and specific capacitive sensor for detection of Gram negative bacteria in a field setting. Recognition of Gramnegative bacteria is based on specific detection of lipopolysaccharides (LPS) by LPS-specific aptamer probe immobilized on electrode sensors. An inhomogeneous AC electric field is applied on sensor electrodes and induces positive dielectrophoresis that attracts LPS particles to the sensor electrodes for rapid detection. The same AC signal is also used to detect the binding reactions occurred on the sensor surface. The AC signal was optimized, and the binding between LPS and the specific aptamer was demonstrated. The detection limit reaches as low as 4.9 fg/mL for free LPS molecules and 53 #/mL of bacteria within a 30s' response time, meeting the needs of onsite bacteria detection.

Rapid, highly sensitive detection of Gram-negative bacteria with lipopolysaccharide based disposable aptasensor.

Gram-negative bacteria are one of the most common microorganisms in the environment. Their differential detection and recognition from Gram-positive bacteria has been attracting much attention over the years. Using Escherichia coli (E. coli) as a model, we demonstrated on-site detection of Gram-negative bacteria by an AC electrokinetics-based capacitive sensing method using commercial microelectrodes functionalized with an aptamer specific to lipopolysaccharides. Dielectrophoresis effect was utilized to enrich viable bacteria to the microelectrodes rapidly, achieving a detection limit of 102 cells/mL within a 30 s' response time. The sensor showed a negligible response to Staphylococcus aureus (S. aureus), a Gram-positive species. The developed sensor showed significant advantages in sensitivity, selectivity, cost, operation simplicity, and response time. Therefore, this sensing method has shown great application potential for environmental monitoring, food safety, and real-time diagnosis.