Research Interests

Wearable Sensors

Thin-Film Transistor Sensing: 

Thin-film transistors (TFT) can be used to build flexible sensors for wearables. However, conventional thin-film transistors are less tolerant to mechanical deformations such as bending and stretching, which limits their application in wearable electronics. We have developed a unique electrochemical approach to fabricate various layered composite thin films consisting of nanomaterials and conducting polymers, called nano-veneers. The nano-veneer sensors are not only flexible but also transparent and adhesive, which makes them easy to be attached for various wearable sensing purposes. 

Colorimetric Array Sensing: 

The colorimetric array sensing approach is a miniaturized and high-throughput chemical sensing platform for the specific and sensitive detection of multiple analytes simultaneously. It configures a flat LED light source, a 2D-sensor cartridge, and a CMOS imager in a tiny “sandwich” structure for colorimetric sensing. Compared to conventional sensing technologies, there are multiple advantages of the 2D-colorimetric array sensing approach: 1)  multiplexed sensing; 2) calibration-free; 3) expandable and configurable; 4) light-weight, miniaturized, and power-efficient, and; 5) capable of continuous monitoring. The unique structure of the 2D-colorimetric array sensor makes it highly compatible with wearable devices. 

Piezoelectric Sensing: 

The micro quartz tuning fork (MQTF) based piezoelectric sensing platform can translate the analytes binding events into resonant oscillating frequency shift. With the advance of film coating technologies, such as molecularly imprinted polymer coating, the surface of MQTF prongs can be modified to achieve high selectivity and specificity to different chemicals. We have developed wireless and cost-effective MQTF-based sensors for detecting both volatile organic compounds (VOCs) and fine particulate matters (PM2.5). Considering MQTFs can be easily integrated into an array for simultaneous detection of multiple pollutants, they can be widely used in wearable platforms for comprehensive personal exposure assessment.

Related Publications:

1. Xiaojun Xian, Liying Jiao, Teng Xue, Zhongyu Wu, Zhongfan Liu. Nanoveneers: An Electrochemical Approach to Synthesizing Conductive Layered Nanostructures, ACS Nano, 5, 4000-4006 (2011)

2. Jingjing Yu, Di Wang, Vishal Varun Tipparaju, Wonjong Jung, and Xiaojun Xian, Detection of Transdermal Biomarkers of Macronutrients Intake Using Gradient-Based Colorimetric Array Sensor, Biosensors and Bioelectronics, 195, 113650 (2022)

3. Laxmi R Jaishi, Jingjing Yu, Wei Ding, Francis Tsow, and Xiaojun Xian*, A Novel Colorimetric Tuning Fork Sensor for Ammonia Monitoring, Sensors and Actuators B-Chemical, 405, 135342 (2024) (https://doi.org/10.1016/j.snb.2024.135342)

4. Laxmi R Jaishi, Wei Ding, Rick A Kittelson, Francis Tsow, and Xiaojun Xian*, Metal-Organic Frameworks (MOFs)-Based Piezoelectric-Colorimetric Hybrid Sensor for Monitoring Green Leaf Volatiles, ACS Sensors, 9, 6553-6562 (2024) (https://doi.org/10.1021/acssensors.4c02016)

5. Amirhossein Amjad, Xiaojun Xian*, Optical Sensors for Transdermal Biomarker Detection: A Review, Biosensors and Bioelectronics, 267, 116844 (2025) (https://doi.org/10.1016/j.bios.2024.116844)