Water-Wettable Open Plasmonic Nanocavities for Ultrasensitive Molecular Detections in Multiple Phases

Capillarity-Driven Enrichment and Hydrodynamic Trapping of Trace Nucleic Acids by Plasmonic Cavity Membrane for Rapid and Sensitive Detections

Small-reactor-based polymerase chain reaction (PCR) has attracted considerable attention. A significant number of tiny reactors must be prepared in parallel to capture, amplify, and accurately quantify few target genes in clinically relevant large volume, which, however, requires sophisticated microfabrication and longer sample-to-answer time. Here, single plasmonic cavity membrane is reported that not only enriches and captures few nucleic acids by taking advantage of both capillarity and hydrodynamic trapping but also quickly amplifies them for sensitive plasmonic detection. The plasmonic cavity membrane with few nanoliters in a void volume is fabricated by self-assembling gold nanorods with SiO2 tips. Simulations reveal that hydrodynamic stagnation between the SiO2 tips is mainly responsible for the trapping of the nucleic acid in the membrane. Finally, it is shown that the plasmonic cavity membrane is capable of enriching severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genes up to 20 000-fold within 1 min, amplifying within 3 min, and detecting the trace genes as low as a single copy µL-1. It is anticipated that this work not only expands the utility of PCR but also provides an innovative way of the enrichment and detection of trace biomolecules in a variety of point-of-care testing applications.

Spectrum and size controllable synthesis of high-quality gold nanorods using 1,7-dihydroxynaphthalene as a reducing agent

The spectrum and size controllable synthesis of gold nanorods is of great value for their widely applicable aspect ratio dependence of anisotropic surface plasmon resonance. Herein, 1,7-dihydroxynaphthalene with a relatively strong reducibility is proposed as a reducing agent for the controllable synthesis of gold nanorods. The result indicated that gold nanorods with high monodispersity, high shape yield, relatively small diameters, and maximum plasmon resonance wavelength of above 1000 nm can be acquired. More importantly, by virtue of the reducing agent used, fine and precise controls over the plasmon wavelength and diameter of the rod can be achieved via changes in experimental conditions. In particular, increases in the concentration of both silver ions and cetyltrimethylammonium bromide (CTAB) can increase the plasmon wavelength from around 600 nm to 1000 nm but respectively show a decreased diameter with the smallest value of around 14.3 nm and a mildly increased diameter from around 9.0 nm to 14.3 nm; moreover, increasing the concentration of reducing agents and gold seeds can simultaneously cause decreases in the plasmon wavelength from around 1000 nm to 800 nm and the diameters from around 14.3 nm to 9.0 and 7.3 nm, respectively. This powerful and efficient method of controllable synthesis of AuNRs could be valuable and attractive for the application of the as-obtained particles.