Label-free and selective cholesterol detection based on multilayer functional structure coated fiber fabry-perot interferometer probe.

A reflective fiber-optic Fabry-Perot cavity probe sensor is proposed to selectively measure cholesterol concentration by insert single mode fiber into ceramic tube and immobilize epoxy resin (ER)/graphene oxide (GO)/beta-cyclodextrin (ß-CD) multi-layer film onto end face of ceramic tube. EDC/NHS activated GO is selected to form chemical binding with ß-CD, and ß-CD is the sensitive materials to bind with cholesterol molecules. With multi-layer film assisted, the sensitivity of sensor to cholesterol concentration can reach 3.92 nm/mM and the limit of detection reaches 3.48 µ M. In addition, 4 mM hemoglobin, glucose and ascorbic acid are doped into a set cholesterol sample and verified the highly selectivity of sensing cholesterol. Furthermore, the reproducibility was proved by measure the spectrum of four sensors with same fabrication process, and the reusability was also proved by repeated measurements. Overall, the sensor features with high mechanical strength, ease of fabrication, real-time monitoring, low cost and ease for measurement that given by probe structure. Therefore, the sensor provides a remarkable analytical platform for biosensing applications.

Reflective epoxy resin/chitosan/PAA composite-functionalized fiber-optic interferometric probe sensor for sensitive heavy metal ion detection.

A highly sensitive label-free chemical sensing platform for the detection of various metal ions is demonstrated. The chemical sensor was derived from a single-mode fiber that is inserted into the ceramic tube with epoxy resin (ER) on the end face for reflecting light and forms the Fabry-Perot (F-P) interferometric cavity. Multilayer chitosan (CS)/polyacrylic acid (PAA) were coated on the surface of the epoxy resin and act as the sensitive film. Based on the analysis of the sensing principle and the F-P cavity structure, the parameters were numerically simulated and experimentally evaluated, which enables ease of fabrication and real-time modulation of the cavity length. The sensitivity of sensing Ni2+, Zn2+, and Na+ reached 9.95 × 10-4 nm ppb-1, 2.31 × 10-4 nm ppb-1, and 4 × 10-4 nm ppb-1, respectively, and the sensing results were theoretically analyzed by the Langmuir adsorption model, which corresponds to the surface atom percentage results obtained by SEM and EDS measurements for sensing three types of metal ions. The proposed ER/CS/PAA multilayer film-coated F-P sensor can be employed as a probe, which features label-free, highly sensitivity, real-time monitoring, ease of measurement, stability, and therefore provides a remarkable analytical platform for chemical applications.

Highly sensitive metal ion sensing by graphene oxide functionalized micro-tapered long-period fiber grating.

An accurate as well as highly sensitive label-free chemical sensing platform for the detection of various metal ions was demonstrated. The chemical sensor was derived from the micro-tapered long-period fiber grating (MLPG) by depositing graphene oxide (GO) by chemical-bonding and optical-tweezer effects. The enhancement in refractive index (RI) sensitivity as well as reusability was obtained by evaluating the deposition thickness in the range of approximately 97.7 to 158.9 nm. Based on the analysis of adsorption principles, the enhanced RI sensitivity leads to a limit of detection as low as 3.2 ppb. The highest sensitivities for the cases studied using sodium and manganese ions in a wide concentration range of 1 ppb to 1 × 106 ppb are respectively 2.2 × 10-3 dB per ppb and 3.2 × 10-3 dB per ppb. Mixture samples were also studied to evaluate the properties of sensing the doped ions. This demonstration of GO modified MLPG is bound to find potential applications that require sensing of mixed samples and illustrates significant importance in developing cost-effective, label-free, reusable, and real-time chemical sensors.

All-optical Ti3C2Tx modulator based on a sandwich structure.

All-optical modulators based on a MXene-Ti3C2Tx have recently garnered much attention due to their broadband light-matter interactions and ultrafast carrier dynamics. To investigate the modulation characteristics of pump intensity and pump light modulation frequency, we establish an all-optical modulator with a sandwich structure based on MXene-Ti3C2Tx/PVA (polyvinyl alcohol) film. The result shows that this modulator can achieve a high modulation depth of 12.55 dB and a modulation frequency of 50 kHz corresponding to a response time at the microsecond scale. The successful preparation of the modulator is attributed to the saturable absorption characteristics of the MXene-Ti3C2Tx. This modulator has great potential in all-optical communications and ultrafast optical signal processing.