Local Electric Potential-Driven Nanofluidic Ion Transport for Ultrasensitive Biochemical Sensing.

Nanofluidic biosensors have been widely used for detection of analytes based on the change of system resistance before and after target-probe interactions. However, their sensitivity is limited when system resistance barely changes toward low-concentration targets. Here, we proposed a strategy to address this issue by means of target-induced change of local membrane potential under relatively unchanged system resistance. The local membrane potential originated from the directional diffusion of photogenerated carriers across nanofluidic biosensors and gated photoinduced ionic current signal before and after target-probe interactions. The sensitivity of such biosensors for the detection of biomolecules such as circulating tumor DNA (ctDNA) and lysozyme exceeds that of applying a traditional strategy by more than 3 orders of magnitude under unchanged system resistance. Such biosensors can specifically detect the small molecule biomarker in the blood sample between prostate cancer patients and healthy humans. The key advantages of such nanofluidic biosensors are therefore complementary to traditional nanofluidic biosensors, with potential applications in a point-of-care analytical tool.

A fuel-initiated DNA molecular machine for microRNA detection in serum via poly-adenine-mediated spherical nucleic acids.

MicroRNAs (miRNAs) have been identified as promising disease diagnostic biomarkers. However, it is challenging to sensitively detect miRNAs, especially in complex biological environments, due to their low abundance and small size. Herein, we have developed a DNA-fueled molecular machine for sensitive detection of miRNA-22 (miR-22) in undiluted serum by combining poly-adenine-mediated spherical nucleic acids (polyA-SNAs) with a toehold mediated strand displacement reaction (TMSDR). The polyA-SNAs are constructed by the assembly of diblock DNA probes on a AuNP surface through the high binding affinity of polyA to AuNPs. The surface density of the diblock DNA probe can be controlled by tuning the length of the polyA block, and the orientation of the diblock DNA probe can adopt an upright conformation, which is beneficial to target hybridization and TMSDRs. TMSDR is an enzyme-free target recycling amplification approach. Taking advantage of polyA-mediated SNAs and TMSDR, the operation of the molecular machine based on two successive TMSDRs on polyA20-SNAs is rapid and efficient, which can significantly amplify the fluorescence response for detection of miR-22 in an undiluted complex matrix. The developed sensor can detect as low as 10 pM of target miRNA/DNA in undiluted fetal bovine serum within 30 min. The synergetic effect of polyA-mediated SNAs and TMSDR presents a potential alternative tool for the detection of biomarkers in real biological samples.

Construction and bioanalytical applications of poly-adenine-mediated gold nanoparticle-based spherical nucleic acids.

Owing to the versatile photophysical and chemical properties, spherical nucleic acids (SNAs) have been widely used in biosensing. However, traditional SNAs are formed by self-assembly of thiolated DNA on the surface of a gold nanoparticle (AuNP), where it is challenging to precisely control the orientation and surface density of DNA. As a new SNA, a polyadenine (polyA)-mediated SNA using the high binding affinity of consecutive adenines to AuNPs shows controllable surface density and configuration of DNA, which can be used to improve the performance of a biosensor. Herein, we first introduce the properties of polyA-mediated SNAs and fundamental principles regarding the polyA-AuNP interaction. Then, we provide an overview of current representative synthesis methods of polyA-mediated SNAs and their advantages and disadvantages. After that, we summarize the application of polyA-mediated SNAs in biosensing based on fluorescence and colorimetric methods, followed by discussion and an outlook of future challenges in this field.