Environmental pollutants, including organic dyes and plastic, have posed severe threats to the health of our ecosystem. Although a lot of efforts have been made to tackle this problem, these pollutants are still massively produced during industrial activities as well as human life. The ability to detect these environmental pollutants with high sensitivity is thus greatly desired. Herein, we propose a novel surface-enhanced Raman spectroscopy (SERS) substrate with high-density hot spots, high Raman signal enhancement, and good uniformity for trace detection of organic pollutants and nanoplastic. The SERS substrates consist of abundant ultranarrow nanogaps that are fabricated with cost-effective colloidal lithography. With the significantly enhanced near-field intensity, rhodamine 6G (R6G) molecules as low as 10u22128 M can be detected with good linear correlations between the signal intensity and molecular concentrations. Moreover, both nanowells and nanogaps are present on the SERS substrates fabricated by our method and the nanowells could be used to trap micro- or nanoplastic. We successfully demonstrate detecting polystyrene (PS) nanospheres (200 nm in diameter) with different concentrations (1.000% to 0.001%), showing the potential to detect micro- or nanoplastic pollutants in the environment. Our method provides a feasible approach to fabricating low-cost SERS substrates for the detection of organic pollutants and nanoplastic.
Accurate micro-force detection is essential for micro-operation and biomedical applications. However, conventional techniques, such as atomic force microscopy (AFM), are bulky and spatially demanding. In this study, we presented micro-spring probes fabricated by femtosecond-laser two-photon polymerization for flexible and precise mechanical sensing. The mechanical stiffness of the probes was tuned by adjusting the spring-wire diameter, with diameters of 2 u00B5m, 2.5 u00B5m, and 3 u00B5m, exhibiting the corresponding micro-force sensitivity of u22120.28 nm/u00B5N, u22120.09 nm/u00B5N, and u22120.07 nm/u00B5N, respectively. The probes enabled accurate measurement of Youngu2019s modulus of the polydimethylsiloxane (PDMS), exhibiting excellent consistency with AFM results. We further proposed a fiber-based self-referenced displacement detection scheme that integrated sensing and reference springs, allowing Youngu2019s modulus characterization without the need for a piezoelectric stage. With the growing development of the u201Clab-on-fiberu201D paradigm, the proposed micro-spring probe provides a promising platform for high-accuracy and compact micro-force sensing.
Respiratory viruses, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A (H1N1), and respiratory syncytial virus (RSV), remain major public health threats due to overlapping clinical symptoms and the limited speed, sensitivity, and multiplexing capacity of conventional diagnostic methods. Here, we present a label-free optical biosensing platform based on subwavelength grating microring resonators (SGMRRs) for the sensitive and specific detection of viral antigens. The sensor surface is functionalized with antibodies against three representative viral proteins, enabling quantitative detection via resonance wavelength shifts upon antigen binding. The platform achieves the refractive index limit of detection (LoD) of 1.25u00D710u22124 RIU and enables the detection of the SARS-CoV-2 spike protein at 100 pg/mL, the H1N1 nucleoprotein at 10 pg/mL, and the RSV F-trimer protein at 10 pg/mL. The compact SGMRR design readily supports multiplexed integration through multi-ring or multi-channel architectures, highlighting its potential as a scalable and high-performance platform for rapid, quantitative, and point-of-care viral diagnostics.
Quasi-distributed smart sensing systems using fiber Bragg grating arrays have found many practical applications in structure health, electricity grid, aerospace, etc. However, the broadband light sources used for the sensing system are generally constrained to the telecom C-band, limiting the available number of sensors, hence hindering deployment of massive sensing heads for the next generation of Internet of Things (IoT) and integrated sensing and communication. Here, we demonstrate a hybrid sensing system enabled by an ultra-broadband Bi/Er co-doped fiber (BEDF) light source pumped at 830 nm. Leveraging the global excitation capability of the u03BB=830 nm pump, the source provides an unprecedented operating bandwidth spanning from O- to L-bands. Quasi-distributed sensing of the temperature and strain for 21 spatially separated nodes is demonstrated using the single BEDF-based Mach-Zehnder interferometer and 20 fiber Bragg gratings. Our proof of the principle system exhibits the maximum temperature sensitivity of 56 pm/u2103 and maximum strain sensitivity of 0.9 pm/u03BCu03B5. To address the issue of the colored noise measured across the spectrum arising from the source itself due to different contributions of varying environmentally sensitive defects responsible for Bi emission, not present in the Er component, we propose the use of data-driven statistical learning methods to quantitatively characterize and mitigate the measurement uncertainties that limit their applicability in precision sensing. Specifically, an adaptive residual bootstrap strategy for uncertainty quantification is used here for the first time, providing a more accurate evaluation of system uncertainty than the conventional normal distribution analysis. The system achieves measurement uncertainties of less than 4.1% for the temperature and 6.4% for the strain. Overall, the proposed sensing system has the huge potential for practical applications in large-scale structural health monitoring, the IoT, etc.
An intensity-interrogated optical fiber hot-wire anemometer employing a cobalt-doped fiber Bragg grating (CD-FBG) is proposed and experimentally demonstrated. The CD-FBG absorbs light energy from a 1480 nm laser and turns into a u201Chot wireu201D with its temperature decreasing and therefore reflection spectrum blue-shifting with the airflow velocity. To achieve intensity interrogation, a wavelength-switchable narrow-linewidth probe laser is used, which makes the reflected optical power from the CD-FBG change monotonously with the airflow velocity in a certain measurement range. In the experiment, the high sensitivity of u22121248 u03BCW/(m/s) is achieved at the airflow velocity of 0.05 m/s. The measurement range is extended to 0 m/su20138.0 m/s by switching the probe laser wavelength. The response time and recovery time of the anemometer are 0.5 seconds and 0.6 seconds, respectively. The intensity interrogation scheme and simple structure of the anemometer probe greatly reduce the cost and make it a promising solution for high-precision airflow velocity measurement in many practical applications.
