On-Fly Femtosecond-Laser Fabrication of Self-Organized Plasmonic Nanotextures for Chemo- and Biosensing Applications

Abstract

Surface-enhanced Raman scattering (SERS) and surface-enhanced photoluminescence (SEPL) are emerging as versatile widespread methods for biological, chemical, and physical characterization in close proximity of nanostructured surfaces of plasmonic materials. Meanwhile, single-step, facile, cheap, and green technologies for large-scale fabrication of efficient SERS or SEPL substrates, routinely demonstrating both broad plasmonic response and high enhancement characteristics, are still missing. In this research, single-pulse spallative micron-size craters in a thick Ag film with their internal nanotexture in the form of nanosized tips are for the first time shown to demonstrate strong polarization-dependent enhancement of SEPL and SERS responses from a nanometer-thick covering Rhodamine 6G layer with average enhancement factors of 40 and 2 × 10(6), respectively. Additionally, the first detailed experimental study is reported for physical processes, underlying the formation mechanisms of ablative nanotextures on such "thick" metal films. Such mechanisms demonstrate a complex "hybrid" fluence-dependent ablation character-appearance of spallative craters, typical for bulk material, at low fluences and formation of upright standing nanotips (frozen nanojets), usually associated with thin-film ablation, in the crater centers at higher fluences. Moreover, special emphasis was made on the possibility to reshape the nanotopography of such spallative craters through multipulse laser-induced merging of their small nanotips into larger ones. The presented approach holds promise to be one of the cheapest and easiest-to-implement ways to mass-fabricate various efficient spallation-nanotextured single-element plasmonic substrates for routine chemo- and biosensing, using MHz-repetition-rate femtosecond fiber laser sources with multiplexed laser-beams.

Fabrication of porous microrings via laser printing and ion-beam post-etching

“…Surface-enhanced Raman scattering (SERS) is an ultra-sensitive non-invasive spectroscopic technique based on a label-free identification of different molecules placed in the vicinity of plasmonic-active nanostructured metallic substrates [1][2][3][4] . Intensity of the characteristic Raman signal defining the specific vibrational signatures of individual molecules is usually very weak.…”

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing

“…2a). It was also reported that the nanoscale morphology of the craters and their plasmonic properties could be tailored via their irradiation with a subsequent laser pulse with properly adjusted energy E 2 [35]. Figure 2(b,c) reveals how the nanoscale surface morphology evolves under irradiation of the imprinted crater with a second laser pulse at E 2 =240 nJ (the energy of the first pulse was fixed at E 1 =430 nJ).…”

“…As a result, the ejected surface layer leaves a crater of a few microns in diameter and with multiple self-organized nanospikes. Such nanospike-based arrangements were shown to act as efficient plasmon-active nanostructures permitting to enhance photoluminescence and SERS signals from the attached emitters [35,36]. The maximum density of such nanospikes within a single crater (which would ensure the best SERS performance) was previously shown to be tuned by the size of the laser beam (or NA of the focusing lens) [36].…”

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing

“…As a result, the ejected surface layer leaves a crater of a few microns in diameter and with multiple self-organized nanospikes. Such nanospike-based arrangements were shown to act as efficient plasmon-active nanostructures permitting to enhance photoluminescence and SERS signals from the attached emitters [36,37]. The maximum density of such nanospikes within a single crater (which would ensure the best SERS performance) was previously shown to be tuned by the size of the laser beam (or NA of the focusing lens) [37].…”

“…Therefore, to ensure a dense arrangement of the craters on the central site of the device without smoothing their surface morphology, we used laser projection lithography to generate a flat-top beam with sharp shoulders and a diameter of 2.5 µm (see Figure 2a). It was also reported that the nanoscale morphology of the craters and their plasmonic properties could be tailored via their irradiation with a subsequent laser pulse with properly adjusted energy E 2 [36]. Figure 2b,c reveals how the nanoscale surface morphology evolves under irradiation of the imprinted crater with a second laser pulse at E 2 = 240 nJ (the energy of the first pulse was fixed at E 1 = 430 nJ, while the time delay between two pulses was 5 ms).…”