Enzyme-Free Plasmonic Biosensor for Direct Detection of Neurotransmitter Dopamine from Whole Blood

Nanoscale directional motion by angustotaxis

Directing motion of a nanoscale object on solid surfaces, in particular in an intrinsic way, is crucial for many aspects of nanotechnology applications. Here we report a novel intrinsic mechanism for nanoscale directional motion, termed angustotaxis, where a wide single walled carbon nanotube in a tapered channel drives itself toward the narrower end of the channel. The underlying physics of angustotaxis is attributed to the lower system potential when the nanotube is at a narrower region of the channel due to the increased contact area between the nanotube and the channel. Angustotaxis could lead to promising routes not only for nanoscale energy conversion from van der Waals potential to mechanical work, but also for mass transport like surface cleaning.

Microfluidics-Implemented Biochemical Assays: From the Perspective of Readout

Over the past decades, microfluidics has emerged as an increasingly important tool to perform biochemical assays for diagnosis and healthcare. The precise fluid control and molecule manipulation within microfluidics greatly contribute to developing assays with simplicity and convenience. The advantages of microfluidics, including decreased consumption of reagents and samples, lower operating and analysis time, much lower cost, and higher integration and automation over traditional systems, offer a great platform to meet the needs of point-of-care applications. In this Review, versatile strategies are outlined and recent advances in microfluidics-implemented assays are discussed from the perspective of readout, because a convenient and straightforward readout is what a biochemical assay requires and the end user desires. Functions and properties arising from each readout are reviewed and the advantages and limitations of each readout are discussed together with current challenges and future perspectives.

Plasmonic biosensors fabricated by galvanic displacement reactions for monitoring biomolecular interactions in real time

Optical sensors are prepared by reduction of gold ions using freshly etched hydride-terminated porous silicon, and their ability to specifically detect binding between protein A/rabbit IgG and asialofetuin/Erythrina cristagalli lectin is studied. The fabrication process is simple, fast, and reproducible, and does not require complicated lab equipment. The resulting nanostructured gold layer on silicon shows an optical response in the visible range based on the excitation of localized surface plasmon resonance. Variations in the refractive index of the surrounding medium result in a color change of the sensor which can be observed by the naked eye. By monitoring the spectral position of the localized surface plasmon resonance using reflectance spectroscopy, a bulk sensitivity of 296 nm ± 3 nm/RIU is determined. Furthermore, selectivity to target analytes is conferred to the sensor through functionalization of its surface with appropriate capture probes. For this purpose, biomolecules are deposited either by physical adsorption or by covalent coupling. Both strategies are successfully tested, i.e., the optical response of the sensor is dependent on the concentration of respective target analyte in the solution facilitating the determination of equilibrium dissociation constants for protein A/rabbit IgG as well as asialofetuin/Erythrina cristagalli lectin which are in accordance with reported values in literature. These results demonstrate the potential of the developed optical sensor for cost-efficient biosensor applications. Graphical abstract.

A facile, solid-state reaction assisted synthesis of a berry-like NaNbO3 perovskite structure for binder-free, highly selective sensing of dopamine in blood samples

Synthesis and fabrication of a berry-like NaNbO₃ perovskite-based modified GCE sensor for the highly selective sensing of dopamine.