A fiber-optic sensor for neurotransmitters with ultralow concentration: near-infrared plasmonic electromagnetic field enhancement using raspberry-like meso-SiO₂ nanospheres

Abstract

The feasibility of a localized surface plasmon resonance (LSPR) enhanced sensor based on raspberry-like nanosphere functionalized silica microfibers has been proposed and experimentally demonstrated. The extinction of single Ag (or Au) nanoparticles usually occurs at visible wavelengths. Nevertheless, a LSPR enhancement at near infrared wavelengths has been achieved by constructing raspberry-like meso-SiO nanospheres with noble metal nanoparticle cluster coating. The nanosphere coating captures γ-amino-butyric acid (GABA) targets through size selectivity and enhances the sensitivity by the LSPR effect. The gathering of GABA on the sensor surface translates the concentration signal to the information of refractive index (RI). Silica microfiber perceives the RI change and translates it to optical signal. The LSPR effect enhances the optical sensitivity by enhancing the evanescent field on the microfiber surface. This combination presents the lowest limit of detection (LOD) of 10 M (three orders lower than that without LSPR enhancement). It could fully afford the detection of ultra-low GABA concentration fluctuation (which is important for determining a variety of neurological and psychiatric disorders). The inherent advantages of the proposed sensors, including their ultra-sensitivity, low cost, light weight, small size and remote operation ability, provide the potential to fully incorporate them into various biomedical applications.

Real‐Time Cellular Cytochrome C Monitoring through an Optical Microfiber: Enabled by a Silver‐Decorated Graphene Nanointerface

“…As the HE 12 mode spreads into the surface coating (Figure S4, Supporting Information), it senses the surface RI change and translates it into a wavelength shift in the interferometric fringe . The surface of the silica microfiber was aminated by sequential modifications with piranha solution and 3‐aminopropyl‐triethoxysilane (APTES) solution ( Figure a), resulting in a surface rich in positive charge . The Ag@RGO nanosheets (The silver nanoparticles were chemically bonded with the RGO nanosheets …”

“…Here, with a thickness of ≈15 nm (according to the AFM image in Figure g), the Ag@RGO nanointerface overlapped with the evanescent field of microfiber, causing its localized electric field to overlap with the evanescent field (Figure b). Therefore, by interacting with the evanescent field of the optical microfiber, the plasmonic electromagnetic field of Ag NPs on nanointerface clearly increased the energy density at the microfiber surface . Because the sensitivity of optical microfiber is proportional to the surface binding‐induced change in propagation constants (Δβ) and Δβ is proportional to the evanescent field of microfiber ( E ), as expressed by Equation , the sensitivity is proportional to the surface energy of the microfiberwhere k 1 and k 2 are constant coefficients.…”

“…To improve the sensitivity and lower the LOD to meet the requirement of in situ cell monitoring, we have constructed a nanointerface with Ag NP‐functionalized reduced graphene oxide (Ag@RGO) between silica microfiber and aptamers (Figure 1a). As a result of the plasmonic electromagnetic field enhancement of Ag NPs,14 as well as the accelerated electron transformation15, 16 and electronic characteristics17 of reduced graphene oxide (RGO), the LOD of the as‐prepared sensor achieved is 6.82 × 10 −17 m , which is five orders of magnitude lower than those of existing electrochemical methods (5.0 × 10 −12 m ),18 six orders of magnitude than those of surface plasmon resonance arrays (5.0 × 10 −11 m ),19 and nine orders of magnitude than both fluorescence methods (2.0 × 10 −8 m )20 and optical microfiber methods without Ag@RGO nanointerface. Such a low LOD meets the requirement of in situ monitoring of the ultralow concentrations of cyt c present outside the cells during the initial step of apoptosis.…”

Label-Free Detection of Cancer Biomarkers Using an In-Line Taper Fiber-Optic Interferometer and a Fiber Bragg Grating

“…New types of optical fiber biosensors have been developed for detecting biomarker in a rapid and label-free manner, showing great potential because of their compact size, easy implementation and diversity in structure. As a promising fiber device, providing high sensitivity due to strong evanescent fields, microfiber interferometer biosensors have been effectively functionalized with biorecognition molecules (oligonucleotides or antibodies) and employed to recognize specific target analytes [ 8 , 9 ]. However, in such microfiber interferometer biosensors, temperature cross-sensitivity usually exists, which leads to undesired perturbation during the process of biological sensing measurement [ 10 ].…”

Recent Advances in the Detection of Neurotransmitters

“…An ultra-sensitive optical sensor for GABA determination was reported by Huang et al [138]. The sensor was based on raspberry-like meso-SiO 2 nanosphere functionalized silica microfibers.…”