Flexible wearable sweat sensors allow continuous, real-time, noninvasive detection of sweat analytes, provide insight into human physiology at the molecular level, and have received significant attention for their promising applications in personalized health monitoring. Electrochemical sensors are the best choice for wearable sweat sensors due to their high performance, low cost, miniaturization, and wide applicability. Recent developments in soft microfluidics, multiplexed biosensing, energy harvesting devices, and materials have advanced the compatibility of wearable electrochemical sweat-sensing platforms. In this review, we summarize the potential of sweat for medical detection and methods for sweat stimulation and collection. This paper provides an overview of the components of wearable sweat sensors and recent developments in materials and power supply technologies and highlights some typical sensing platforms for different types of analytes. Finally, the paper ends with a discussion of the challenges and a view of the prospective development of this exciting field.

Countless waveguides have been designed based on four basic bends: circular bend, sine/cosine bend, Euler bend (developed in 1744) and Bezier bend (developed in 1962). This paper proposes an n-adjustable (NA) bend, which has superior properties compared to other basic bends. Simulations and experiments indicate that the NA bends can show lower losses than other basic bends by adjusting n values. The circular bend and Euler bend are special cases of the proposed NA bend as n equals 0 and 1, respectively. The proposed bend are promising candidates for low-loss compact photonic integrated circuits.

The integration density of photonic integrated circuits (PICs) is significantly limited by the waveguide bend losses. Reducing waveguide losses by design of the geometry of waveguide bends is important for photonic integrated circuits. Currently, circular bend and Euler bend are the two most common bends used in bending waveguide designs. A modified n -adjustable bend is proposed for ultra-small radius (≤2 µm) by applying the widening width method to n -adjustable bends. Simulations and experiments indicate that the modified n -adjustable bends show excellent performances in bend loss when the radius is 0.5, 1.0, 1.5, and 2.0 µm. In the experiments, the reduction of measured bend loss was from 0.8197 dB/90° (Euler bend) to 0.0689 dB/90° (modified n -adjustable bend) when radius equals 1.0 μm, and from 0.1438 dB/90° (Euler bend) to 0.0167 dB/90° (modified n -adjustable bend) when radius equals 2.0 μm. The modified n -adjustable bends are potential candidates for waveguide components in ultra-compact photonic integrated circuits.

A miniature Fourier transform spectrometer is proposed using a thin-film lithium niobate electro-optical modulator instead of the conventional modulator made by titanium diffusion in lithium niobate. The modulator was fabricated by a contact lithography process, and its voltage-length and optical waveguide loss were 2.26 V·cm and 1.01 dB/cm, respectively. Based on the wavelength dispersion of the half-wave voltage of the fabricated modulator, the emission spectrum of the input signal was retrieved by Fourier transform processing of the interferogram, and the analysis of the experimental data of monochromatic light shows that the proposed miniaturized FTS can effectively identify the input signal wavelength.