Polymer materials exhibit unique properties in the fabrication of optical waveguide devices, electromagnetic devices, and bio-devices. Direct laser writing (DLW) technology is widely used for micro-structure fabrication due to its high processing precision, low cost, and no need for mask exposure. This paper reviews the latest research progresses of polymer-based micro/nano-devices fabricated using the DLW technique as well as their applications. In order to realize various device structures and functions, different manufacture parameters of DLW systems are adopted, which are also investigated in this work. The flexible use of the DLW process in various polymer-based microstructures, including optical, electronic, magnetic, and biomedical devices are reviewed together with their applications. In addition, polymer materials which are developed with unique properties for the use of DLW technology are also discussed.

Using fusion splicing and hydroxide catalysis bonding (HCB) technology, an all-silica inline fiber-optic sensor with high-pressure survivability, high-resolution salinity measurement capability, and corrosion resistance for deep sea explorations is proposed and experimentally demonstrated. Two extrinsic Fabry-Perot interferometers (EFPIs) and a fiber Bragg grating (FBG) are cascaded in one single-mode fiber (SMF), enabling structural integration of single lead-in fiber and versatility of the sensing probe for temperature, depth, and salinity monitoring. The HCB technology offers a polymer adhesive-free assembly of one open-cavity EFPI for refractive index (RI) (salinity) sensing under normal pressure and temperature (NPT) conditions, showing obvious advantages of strong bonding strength, reliable effectiveness, and no corrosive chemicals requirements. The other EFPI formed by a fused structure is designed for pressure (depth) measurement. The cascading of EFPIs, especially the open-cavity EFPI immersed in water, will result in large light transmission loss and bring challenges to signal interrogation. Graded-index fiber (GIF) micro-collimators and reflective films are added to prevent dramatic degradations of signal intensity and fringe visibility underwater. Thereby, a Fabry-Perot (FP) cavity of several hundreds of microns in length and an open cavity of a thousand microns can be cascaded for underwater applications, effectively enhancing sensitivities and underwater signal readout simultaneously. Results show that the proposed sensor can well operate in the deep-sea pressure range of 0∼2039.43 mH₂O, RI range of 1.33239∼1.36885 RIU, and temperature range of 23∼80 °C, with resolutions of 0.033 MPa, 4.16×10⁻⁷ RIU, and 0.54 °C, respectively. With the multi-parameter measurement capability, all-silica construction, and inline compact structure, the proposed sensor could be a potential candidate for deep sea exploration.

In this paper, a tilted fiber Bragg grating (TFBG) plasmonic sensor based on thymine (T) - Hg - thymine (T) (T-Hg-T) base asymmetric pairing and Au nanoparticles (AuNPs), which can be used for highly sensitive and selective ultra-low-concentration Hg2+ detection, has been demonstrated. As is known, TFBG can provide an effective mean to easily excite the surface plasmon resonance (SPR) phenomenon while the fiber is coated with metal layer. By measuring the evolution of spectra, the SPR properties hence the surface perturbation could be detected accurately. To achieve highly sensitive and selective Hg2+ detection, the two specially designed single-strand probe DNAs (ssDNAs) with rich T base that can specifically forming stable T-Hg-T asymmetric pairing are served as a binding element for AuNPs labelled-target DNA conjugates. In the present of Hg2+, these two ssDNAs that modified respectively on the surface of the sensor and the AuNPs will create a double helix T-Hg-T structure between the two DNA oligonucleotides and result in the surface refractive index perturbation amplified by the AuNPs. To overcome the low reusability of the AuNPs based DNA biosensor, by using iodide ions that can form more stable compounds with mercury ions over the T-Hg2+-T structure, a regenerable DNA biosensor that can repeatedly detect mercury ions is developed. The experimental results demonstrate that this sensor shows an excellent ultra-low-concentration and selectivity detection capability for Hg2+ with the limit of detection (LOD) of ${3.073 \times 10^{-12} M \ (3.073 pM)}$ as well as a large dynamic range of 8 order of magnitude from ${1.0\times 10^{11}\rm \ M \ to \ {1.0\times 10^{3}} M}$ simultaneously. Thus, the experimental results in various actual sample from ultrapure/tap water to even clinical human serum, also reveal that it has potential application for Hg2+ detection in environmental samples and in clinic biological samples.

A miniature fiber-optic tip Fabry-Perot (FP) pressure sensor with excellent high-temperature survivability, assembled by hydroxide catalysis bonding (HCB) technology, is proposed and experimentally demonstrated. A standard single-mode fiber is fusion spliced to a fused silica hollow tube with an outer diameter (OD) of 125 µm, and a 1-µm-thick circular silicon diaphragm with a diameter slightly larger than the OD is bonded to the other endface of the hollow tube by HCB technology. The ultrathin silicon diaphragm is prepared on a silicon-on-insulator (SOI) wafer produced by microelectromechanical systems (MEMS), providing the capability of large-scale mass production. The HCB technology enables a polymer-free bonding between diaphragm and hollow tube on fiber tip with the obvious advantages of high alignment precision, normal pressure and temperature (NPT) operation, and reliable effectiveness. The static pressure and temperature response of the proposed sensor are discussed. Results show that the sensor has a measurable pressure range of 0∼100 kPa, which is well consistent with the measurement range of biological blood pressure. The pressure sensitivity is up to 2.13 nm/kPa with a resolution of 0.32% (0.32kPa). Besides, the sensor possesses a unique high-temperature resistant capability up to 600 °C, which can easily survive even in high-temperature sterilization processes, and it has a low temperature dependence of 0.09 kPa/°C due to the induced HCB bonding technology and the silicon-based diaphragm. Thus, the proposed fiber tip pressure sensor is desirable for invasive biomedical pressure diagnostics and pressure monitoring in related harsh environments.

We proposed and demonstrated a novel tilted fiber Bragg grating (TFBG)-based surface plasmon resonance (SPR) label-free biosensor via a special boronic acid derivative to detect glycoprotein with high sensitivity and selectivity. TFBG, as an effective sensing element for optical sensing in near-infrared wavelengths, possess the unique capability of easily exciting the SPR effect on fiber surface which coated with a nano-scale metal layer. SPR properties can be accurately detected by measuring the variation of transmitted spectra at optical communication wavelengths. In our experiment, a 10° TFBG coated with a 50 nm gold film was manufactured to stimulate SPR on a sensor surface. To detect glycoprotein selectively, the sensor was immobilized using designed phenylboronic acid as the recognition molecule, which can covalently bond with 1,2- or 1,3-diols to form five- or six-membered cyclic complexes for attaching diol-containing biomolecules and proteins. The phenylboronic acid was synthetized with long alkyl groups offering more flexible space, which was able to improve the capability of binding glycoprotein. The proposed TFBG-SPR sensors exhibit good selectivity and repeatability with a protein concentration sensitivity up to 2.867 dB/ (mg/mL) and a limit of detection (LOD) of 15.56 nM.