All-dielectric resonant micro- and nano-structures made of high-index dielectrics have recently emerged as a promising surface-enhanced Raman scattering (SERS) platform which can complement or potentially replace the metal-based counterparts in routine sensing measurements. These unique structures combine the highly-tunable optical response and high field enhancement with the non-invasiveness, i.e. chemically non-perturbing the analyte, simple chemical modification and recyclability. Meanwhile, commercially competitive fabrication technologies for mass production of such structures are still missing. Here, we attest a chemically inert black silicon (b-Si) substrate consisting of randomly-arranged spiky Mie resonators for a true non-invasive (chemically non-perturbing) SERS identification of the molecular fingerprints at low concentrations. Based on the comparative in situ SERS tracking of the para-aminothiophenol (PATP)-to-4,4′-dimercaptoazobenzene (DMAB) catalytic conversion on the bare and metal-coated b-Si, we justify the applicability of the metal-free b-Si for ultra-sensitive non-invasive SERS detection at a concentration level as low as 10⁻⁶ M. We performed supporting finite-difference time-domain (FDTD) calculations to reveal the electromagnetic enhancement provided by an isolated spiky Si resonator in the visible spectral range. Additional comparative SERS studies of the PATP-to-DMAB conversion performed with a chemically active bare black copper oxide (b-CuO) substrate as well as SERS detection of the slow daylight-driven PATP-to-DMAB catalytic conversion in the aqueous methanol solution loaded with colloidal silver nanoparticles (Ag NPs) confirm the non-invasive SERS performance of the all-dielectric crystalline b-Si substrate. A proposed SERS substrate can be fabricated using the easy-to-implement scalable technology of plasma etching amenable on substrate areas over 10 × 10 cm² making such inexpensive all-dielectric substrates promising for routine SERS applications, where the non-invasiveness is of high importance.

We report an easy-to-implement device for surface-enhanced Raman scattering (SERS)-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct femtosecond (fs)-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie–Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site. The efficient pre-concentration of the analyte onto the sensor site based on densely arranged spiky plasmonic nanotextures results in its subsequent label-free identification by means of SERS spectroscopy. Using the proposed device, we demonstrate reliable SERS-based fingerprinting of various analytes, including common organic dyes and medical drugs at ppb concentrations. The proposed device is believed to find applications in various areas, including label-free environmental monitoring, medical diagnostics, and forensics.

Direct laser reshaping of nanostructures is a cost-effective and fast approach to create or tune various designs for nanophotonics. However, the narrow range of required laser parameters along with the lack of in-situ temperature control during the nanostructure reshaping process limits its reproducibility and performance. Here, we present an approach for direct laser nanostructure reshaping with simultaneous temperature control. We employ thermally sensitive Raman spectroscopy during local laser melting of silicon pillar arrays prepared by self-assembly microsphere lithography. Our approach allows establishing the reshaping threshold of an individual nanostructure, resulting in clean laser processing without overheating of the surrounding area.

Ultrashort laser pulses deliver electromagnetic energy to matter causing its localized heating that can be used for both material removal via ablation/evaporation and driving interface chemical reactions. Here, it is shown that both mentioned processes can be simultaneously combined within straightforward laser nanotexturing of Si wafer in a functionalizing solution to produce a practically relevant metal–semiconductor surface nano‐morphology. Such unique hybrid morphology represents deep‐subwavelength Si laser‐induced periodic surface structures (LIPSSs) with an extremely short period down to 70 nm and high‐aspect‐ratio nano‐trenches loaded with controllable amount of plasmonic nanoparticles formed via laser‐induced decomposition of the precursor noble‐metal salts. Moreover, heat localization driving reduction process is utilized to produce surface morphology locally decorated with dissimilar plasmon‐active nanoparticles. Light‐absorbing deep‐subwavelength Si LIPSSs loaded with controllable amount of noble‐metal nanoparticles represent an attractive architecture for plasmon‐related applications such as optical nanosensing where efficient coupling of the propagating optical waves to highly localized electromagnetic “hot spots” is a mandatory requirement. To support this statement, applicability of such hybrid morphology for fluorescence‐based detection of nanomolar concentrations of mercury cations in solution is demonstrated.

Incorporation of Ge into Si _1−x Ge _x nanoparticles allows modification of their light-to-heat conversion and optical response, which is crucial for biosensing applications.