Spectroscopy Journal

Candida auris is an emerging fungal pathogen associated with healthcare outbreaks, invasive infections, environmental persistence, and antifungal resistance. Rapid strain characterization may support epidemiological surveillance, but conventional identification workflows can require specialized instrumentation and updated databases. This proof-of-concept study evaluated near-infrared (NIR) spectroscopy combined with Data-Driven Soft Independent Modeling of Class Analogy (DD-SIMCA) for authenticating a reference strain representing Clade I. Four reference strains representing Clades I–IV were cultured under standardized conditions, and 200 diffuse-reflectance spectra were acquired from 900 to 2600 nm. The Clade I model yielded sensitivities of 91.43% for the training set and 100% for the test set under spectrum-level partitioning. To assess performance using independent culture plates, a plate-separated analysis was performed using seven plates for training and three separate plates for testing, yielding test sensitivities ranging from 46.7% to 80%. Specificity was 100% for the strains representing Clades III and IV and 64% for the strain representing Clade II under spectrum-level partitioning, whereas plate-separated specificity for the Clade II representative ranged from 42% to 54%. These findings are consistent with greater spectral overlap between the Clade I and II representatives and support the analytical feasibility of NIR/DD-SIMCA for rapid, culture-based screening. Because only one reference strain represented each clade, validation with multiple independent isolates, culture batches, instruments, and laboratories is required before clade-level or clinical use.

Recent advances have broadened the capabilities of continuous-wave cavity ring-down spectroscopy (CW-CRDS), driven by demands for higher sensitivity, faster acquisition, and reliable operation in non-ideal environments. From the emergence of CW-CRDS in the late 1990s to developments reported through August 2026, this review traces changes in resonator architecture, resonance control, and acquisition strategies. Drawing on 171 cited sources, this narrative review organizes progress through a taxonomy spanning (i) cavity and coupling architectures, including compact resonators, related fiber-based systems, extended spectral implementations, and multiplexed or comb-enabled designs; (ii) ring-down acquisition and modulation approaches, ranging from controlled and random cavity-length tuning to coding-based and hybrid modulation–absorption schemes, with different trade-offs in spectral coverage and drift sensitivity; and (iii) analysis workflows that address precision and traceability, such as Allan-variance-guided optimization, saturation/nonlinearity modeling, and uncertainty reporting. We connect these technical choices to key application areas, including trace-gas sensing, reactive and transient media, particulate/aerosol measurements, breath analysis, and precision spectroscopy. Deployment considerations, including sampling interfaces, long-term stability, and calibration transfer, are discussed for harsh or space-limited settings. Remaining challenges in mode matching, baseline control, scalable multiplexing, and low-power integration are outlined to guide next-generation CW-CRDS instruments.

Polarizers are essential optical components for spectroscopic measurement, hyperspectral imaging and polarimetric detection over the past two decades. However, the wide variety of polarizers, characterization strategies, and spectroscopic applications has made it difficult to compare their properties directly and to identify their respective merits and limitations clearly. In this review, the development of polarizers and polarization spectroscopy is initially summarized. Then, the structures, working mechanisms, fabrication strategies and characterization methods of three representative types of functional thin-film polarizers: polyvinyl alcohol (PVA)-I₂ polarizers, low-symmetry two-dimensional (2D) functional polarizers (Graphene, Black phosphate, transition metal dichalcogenides (TMDCs)), and sub-wavelength wire-grid polarizers (WGPs) will be discussed systematically. The advantages and intrinsic bottlenecks of these three polarizer types will be compared for concrete spectroscopy-relevant scenarios from all sorts of directions. Afterwards, the gap between optimal structural design and performance improvement is addressed through a summarized methodology based on Mueller–Stokes polarimetry and the Poincaré sphere. Furthermore, characterization techniques, mechanistic insights, and potential applications of polarizers and polarization spectroscopy are presented in these findings, which offer a comprehensive strategy for designing novel structures and inspire future research on next-generation functional thin films for optical displays, molecular structural analysis, polarization imaging and polarization photodetectors.