Search for: All records

Abstract Surface‐enhanced Raman scattering (SERS) sensors typically employ nanophotonic structures that support high‐field confinement and enhancement in hotspots to increase the Raman scattering from target molecules by orders of magnitude. In general, high field and SERS enhancement can be achieved by reducing the critical dimensions and mode volumes of the hotspots to nanoscale. To this end, a multitude of SERS sensors employing photonic structures with nanometric hotspots have been demonstrated. However, delivering analyte molecules into nanometric hotspots is challenging, and the trade‐off between field confinement/enhancement and analyte delivery efficiency is a critical limiting factor for the performance of many nanophotonic SERS sensors. Here, a new type of SERS sensor employing solid‐metal nanoparticles and bulk liquid metal is demonstrated to form nanophotonic resonators with a nanoparticle‐on‐liquid‐mirror (NPoLM) architecture, which effectively resolves this trade‐off. In particular, this unconventional sensor architecture allows for the convenient formation of nanometric hotspots by introducing liquid metal after analyte molecules are efficiently delivered to the surface of gold nanoparticles. In addition, a cost‐effective and reliable process is developed to produce gold nanoparticles on a substrate suitable for forming NPoLM structures. These NPoLM structures achieve two orders of magnitude higher SERS signals than the gold nanoparticles alone. 

We demonstrate ultrastrong coupling between intersubband transitions in single semiconductor quantum well and resonant modes of photonic nanocavities implemented on both rigid and flexible substrates. The Rabi splitting reaches 27% of the intersubband transition frequency. 

Abstract Nanophotonic resonators can confine light to deep-subwavelength volumes with highly enhanced near-field intensity and therefore are widely used for surface-enhanced infrared absorption spectroscopy in various molecular sensing applications. The enhanced signal is mainly contributed by molecules in photonic hot spots, which are regions of a nanophotonic structure with high-field intensity. Therefore, delivery of the majority of, if not all, analyte molecules to hot spots is crucial for fully utilizing the sensing capability of an optical sensor. However, for most optical sensors, simple and straightforward methods of introducing an aqueous analyte to the device, such as applying droplets or spin-coating, cannot achieve targeted delivery of analyte molecules to hot spots. Instead, analyte molecules are usually distributed across the entire device surface, so the majority of the molecules do not experience enhanced field intensity. Here, we present a nanophotonic sensor design with passive molecule trapping functionality. When an analyte solution droplet is introduced to the sensor surface and gradually evaporates, the device structure can effectively trap most precipitated analyte molecules in its hot spots, significantly enhancing the sensor spectral response and sensitivity performance. Specifically, our sensors produce a reflection change of a few percentage points in response to trace amounts of the amino-acid proline or glucose precipitate with a picogram-level mass, which is significantly less than the mass of a molecular monolayer covering the same measurement area. The demonstrated strategy for designing optical sensor structures may also be applied to sensing nano-particles such as exosomes, viruses, and quantum dots.