A nanothin block copolymer (BCP) brush-layer film adsorbed on glass nanofibers is shown to address the longstanding challenge of forming a template for the deposition of dense and well-dispersed nanoparticles on highly curved surfaces, allowing the development of an improved nanosensor for neurotransmitters. We employed a polystyrene-block-poly(4-vinylpyridine) BCP and plasmonic gold nanoparticles (AuNPs) of 52 nm in diameter for the fabrication of the nanosensor on pulled fibers with diameters down to 200 nm. The method is simple, using only solution processes and a plasma cleaning step. The templating of the AuNPs on the nanofiber surprisingly gave rise to more than 1 order of magnitude improvement in the surface-enhanced Raman scattering (SERS) performance for 4mercaptobenzoic acid compared to the same AuNPs aggregated on identical fibers without the use of a template. We hypothesize that a wavelength-scale lens formed by the nanofiber contributes to enhancing the SERS performance to the extent that it can melt the glass nanofiber under moderate laser power. We then show the capability of this nanosensor to detect the corelease of the neurotransmitters dopamine and glutamate from living mouse brain dopaminergic neurons with a sensitivity 1 order of magnitude greater than with aggregated AuNPs. The simplicity of fabrication and the far superior performance of the BCP-templated nanofiber demonstrates the potential of this method to efficiently pattern nanoparticles on highly curved surfaces and its application as molecular nanosensors for cell physiology.

We present a dual-resonance fiber surface plasmon resonance (SPR) sensor for biological analysis. The sensing element was fabricated by sequentially sputtering layers of indium tin oxide (ITO) (100 nm thickness) and Au (35 nm thickness) on the surface of an optical fiber. The refractive index dispersion effect of ITO material led to resonances in the near infrared and visible wavelength regions. The refractive index of ITO is larger than the optical fiber in visible spectral area (400 to 733nm), such that the structure is a typical Kretschmann configuration surface plasmon resonance sensor. However, an Otto configuration is observed in the near infrared area (NIR) due to the ITO refractive index being smaller than the fiber core. We characterized the sensor performance by measuring bulk refractive index (RI) sensitivity in the two configurations, which were 1345 nm/RIU in the Kretschmann configuration and 1100 nm/RIU in the Otto configuration. In addition, this sensor was applied for real-time and label-free monitoring of the IgG/anti-IgG biomolecular interaction. As a robust and ultra-compact SPR sensor, which possesses wide detection range and is highly sensitive, this fiber SPR sensor can be applied for real-time biological analysis and monitoring.

safety, and environmental monitoring, owing to their stronger near-field confined capacity on the surface, as compared with that of prism-based metallic film sensors. [1][2][3][4][5][6][7][8][9][10][11] Moreover, surface plasmon resonance (SPR) in plasmonic nanostructures can be directly excited by using simple free-space incident light instead of complex and bulky optical prism excitation systems, which exhibits great potential for developing ultracompact and multiplexed sensing applications. [12][13][14][15] Many efforts have been focused on engineering the topography and materials of nanostructures to improve their sensitivity and to realize portable sensing applications, such as nanoholes, [16][17][18] nanodisks, [19][20][21] nanorings, [22,23] and nanomushroom arrays. [24] To date, most plasmonic nanostructure sensors have been fabricated by lithography-based top-down nanofabrication technologies, for example, focused ion beam milling [25,26] and electron beam lithography. [19][20][21][22][23][24] Although they have high preparation precision, good stability, and repeatability, these top-down nanofabrication technologies suffer from some inherent shortcomings, such as high equipment cost, time-consuming fabrication, low yields, and small footprint sizes (usually limited to below 100 µm × 100 µm), which severely restrict the practical applications of plasmonic nanostructure sensors. In addition, because of the abovementioned small sensor footprint, the angle-dependent sensing properties are relatively less studied. [27][28][29] To overcome these drawbacks, bottom-up nanofabrication technologies, such as nanosphere lithography and tunable holographic lithography, are used to generate large-scale ordered nanostructure arrays with low cost and facile fabrication. [30,31] However, large-scale fabrication approaches are mainly used to fabricate sunken nanostructures, such as nanoholes or nanogrooves. [28,31,32] The relatively low sensing capabilities of sunken nanostructures make them uncompetitive with those of prism-based SPR sensors. Therefore, there is an urgent demand for the realization of large-scale, low cost biosensors with convex nanostructures, such as large scale fabrication of nanostructures by laserinduced dewetting and laser ablation methods. [33,34] In this paper, we reported a centimeter-scale, convex plasmonic nanostructure as a sensing platform fabricated by low cost transfer nanoprinting and based on an ultrathin anodic Surface plasmon resonance in plasmonic nanostructures has become a powerful analytical tool in ultrasensitive label-free biomolecule sensing. However, the fabrication of plasmonic nanostructure sensors relies on lithography-based top-down nanofabrication approaches, which have inherent shortcomings, such as high manufacturing cost, time-consuming fabrication, and a small fabrication footprint. In particular, the small footprint of fabricated plasmonic nanostructures has significantly restrained the study of their angle-dependent sensitivity. Here, a centimeter-scale, high sensit...