Surface-enhanced Raman scattering (SERS) provides a novel method for low concentration molecular detection. The performances were highly dependent on the sizes, geometries and distributions of metal nanostructures. Here, highly sensitive SERS fiber probe based on silver nanocubes (Ag NCs) was fabricated, by assembled nanostructures on planar and tapered fiber tips. Ag NCs were synthesized by polyol method, and controlled by reductant content, reaction temperatures and crystal growth durations. Tapered fibers with different cone angles were prepared by chemical etching. The electromagnetic distribution simulation indicated that nanocubes had stronger electric field between two cubes and vertex corners than nanosphere, under 532 nm laser excitation. The intensity could reach 53.52 V/m, for cubes with 70 nm edge length. The SERS performance of probes was characterized using crystal violet analyte. The detectable lowest concentration could reach 10–9 and 10–10 M for planar and tapered fiber probes, respectively. The corresponding enhancement factor could be 9.02 × 107 and 6.22 × 108. The relationship between SERS peak intensities and analyte concentrations showed well linear, which indicated both fiber probes could be applied for both qualitative and quantitative analysis. Furthermore, optimal cone angle of tapered fiber SERS probe was 8.3°. The tapered fiber SERS probes have highly sensitive activity and great potential in substance detection.
Fiber-optic anemometers have attracted an increasing attention over the past decade owing to their high sensitivity, wide dynamic range, low power consumption, and immunity to electromagnetic interference. However, expensive instruments may limit their practical applications. Herein, a new type of airflow sensor based on optical micro/nanofiber (MNF) is proposed and realized. The sensing element is a flexible polydimethylsiloxane (PDMS) cantilever embedded with a U-shaped MNF. Upon exposure to airflow, the induced deflection of the cantilever results in a bending-dependent transmittance variation of the embedded MNF. The performance of the sensor can be engineered by tuning the cantilever thickness and/or the MNF diameter. When four cantilevers are arranged in two orthogonal directions, the transmittance of each cantilever will be dependent on both flow speed and direction. By analysing the output signals of the four cantilevers, omnidirectional airflow with flow speed within 15 m/s were experimentally measured. In addition, a variety of voice and respiratory signals can be monitored and distinguished in real-time using an optimized cantilever with a resolution of 0.012 m/s, presenting great potential for health monitoring applications.
With the rapid development of internet of things and wearable electronics, how to conveniently power uncountable sensors remains a huge challenge. Energy harvesting strategy is suggested to collect and convert environmental energies into electrical energy. Thereinto, piezoelectric polymers are utilized as flexible harvesters to convert mechanical energy. The latter widely distributes in both our daily life and industrial environment. Intrinsic piezoelectric property further drives piezoelectric polymers to construct flexible self-powered strain sensors. However, relatively low piezoelectric performance restricts their application in detection and conversion of weak mechanical excitations. Herein, wave-shaped 3D piezoelectric device was fabricated by embossing electrospun polyvinylidene fluoride nanofibers. This 3D structured device presents better longitudinal and transverse piezoelectric performance than usual flat-type one. This wave-shaped piezoelectric device was developed for acoustic detection and recognition with a frequency resolution better than 0.1 Hz. This wave-shaped device was capable of frequency spectrum analyses of various sound sources from human and animals and well presents its potential for future wearable acoustic sensors and transducers.
Stimuli-responsive fusion and fission are widely observed in both bio-organizations and artificial molecular assemblies. Recently, Professor Gao’s group in Zhejiang University discovered and explained an interesting phenomenon that precisely reversible fusion and fission in a bundle of wet-spun graphene oxide fibers is possible. It provides a new model to uncover the dynamic assembly of macroscopic soft materials. This study hopefully inspires further research in engineering structural materials, as well as fields requiring a stimuli-responsive and dynamic system.
Organ-on-a-chip (OOC) is now becoming a potential alternative to the classical preclinical animal models, which reconstitutes in vitro the basic function of specific human tissues/organs and dynamically simulates physiological or pathological activities in tissue and organ level. Despite of the much progress achieved so far, there is still an urgent need to explore new biomaterials to construct a reliable and efficient tissue–tissue interface and a general fabrication strategy to expand from single-organ OOC to multi-organ OOC in an easy manner. In this paper, we propose a novel strategy to prepare double-compartment organ-on-a-chip (DC-OOC) using electrospun poly(l-lactic acid)/collagen I (PLLA/Col I) nanofiber membrane as tissue–tissue interface. The unique features of PLLA/Col I nanofiber membrane like excellent biocompatibility, strong affinity to multiple cells, adjustable orientation, controllable thickness and porosity endow the tissue–tissue interface with excellent semi-permeability, appropriate mechanical support, inducible cell orientation, good cell adhesion and proliferation. The integration of 3D printing technology during the fabrication process enables precise size control of the tissue–tissue interface and stable bonding with microfluidic channels. More importantly, our fabrication strategy and OOC configuration makes it easy to extend from DC-OOC to multi-compartment organ-on-a-chip (MC-OOC). To show its possible application, in vitro jaundice disease model is established by constructing blood vessel/skin/liver/lung organ-on-a-chip via MC-OOC. The downward trends of the cell viability after perfusion of bilirubin, the variation in cell sensitivity to bilirubin for different type of cells and recovery of cell viability after blue light therapy prove the feasibility of this jaundice disease model. We believe this general strategy of constructing tissue–tissue interface and multi-organ OOC can be used for many other in vitro physiological and pathological models.
a Schematic illustration on fabrication process of DC-OOC; b construction of blood vessel/skin/liver/lung organ-on-a-chip as in vitro jaundice disease model
Rapid development in wearable electronics has brought huge convenience to human life and gradually penetrated into various indispensable fields, such as health monitoring, medical assistance, smart sports, object tracking and smart home, etc. However, the suitable energy supply system for these wearable electronics remains an important issue to address. Fiber and textile triboelectric nanogenerators (f/t-TENGs), capable of converting biomechanical energy into electricity, have promising features to act as a mobile sustainable power source for wearable electronics or directly serve as an intelligent self-powered sensing solution. Compared with the low-output piezoelectric nanogenerators, hard-to-wear electromagnetic generators and other bulk TENGs, the fiber/textile TENG may be the best type of wearable human mechanical energy harvester at present. Herein, this review comprehensively introduces the recent progress of smart fibers and textiles with a highlight on triboelectric nanogenerators, including the general materials and structures of fiber/textile shaped electronics, various fiber and textile devices for triboelectric/triboelectric-integrated energy harvesting and self-powered smart sensing systems. Moreover, the advance of f/t-TENGs with multifunctionality and large-scale textile processing techniques is summarized as well. Finally, the challenges and perspectives of f/t-TENGs for future improvement, large-scale production and emerging applications are thoroughly discussed as well.