Projects
I have done projects spanning optics, microrobots, wearable and flexible electronics, sensors and even plant science.
Autonomous sweat sensor for wide-spectrum detection of metabolites and nutrients
Building on the laser-engraved graphene technology, we have further widened the detection spectrum of wearable sweat sensing using a universal sensing strategy based on molecularly imprinted polymers that function as "artificial antibodies". Based on this sensing strategy, we have enabled the detection of previously undetectable amino acids, vitamins,
drugs, and nutrients. Besides enhanced sensing, we also devised a mass-producible microfluidic module with numerically optimized geometry and developed an autonomous sweat induction module within the same form factor to achieve on-demand sweat stimulation and sampling at rest without exercise. Collaborating with Prof. Zhaoping Li from UCLA clinical nutrition, we have applied this invention to pilot studies for monitoring branched-chain amino acids (BCAAs) for metabolic syndrome management and COVID-19 severity evaluation. Furthermore, we are implementing this technology for pilot studies in drug-dosing monitoring at the City of Hope, collaborating with Prof. Jeannine McCune.
Laser-engraved graphene patch for metabolic monitoring
Instead of using commercial electrodes that could barely detect trace metabolites in sweat without expensive modifications, we have applied laser-engraving to fabricate a patch that encorporate graphene sensors for ultralow metabolite monitoring and multiplexed vital sign detection with efficient sweat-sampling
microfluidics. The patch was further integrated with flexible PCB for signal conditioning, processing and wireless data transmission to user interface. Using this patch, we have demonstrated the first-ever continuous monitoring of trace metabolites, uric acid (hallmark biomarker of gout) and tyrosine, in human sweat in vivo.
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Gout is an inflammatory arthritis and affects millions of Americans. Elevation in serum uric acid (UA) could trigger an gout attack, and there's an urgent need to continuously monitor UA and help gouty individuals to make informed food choice to avoid spikes in UA levels. Collaborating with Prof. Zhaoping Li at UCLA Medical Center (chief of Clinical Nutrition), we are evaluating our wearable systems for personalized management of various metabolic disorders. We have successfully applied our wearable sensor in healthy individuals as well as gout patients and hyperuricemia. The high sweat-serum uric acid correlation obtained with the LEG sensor has shown promising potentials of using the wearable LEG sensor for continuous UA monitoring for metabolic health monitoring.
Laser-engraved graphene patch for stress monitoring
The increased pace of life in the 21st century constantly demands intense mental and physical efforts for individuals and could trigger stress. The stress and individuals’ stress-coping is a dynamic process, and an absolute quantification of stress levels offers rich information and great diagnostic values. Current stress evaluation process relies heavily on subjective questionnaires and diary studies, which is subjective to idiosyncrasy imposed by individuals’ interpretation; thus
the accuracy of such “stress assessment” could be insufficient. Stress hormones, such as cortisol, on the other hand, provide great quantitative measure of stress levels as well as pain and fear sensations. However, the sampling process of the stress hormones is still mostly based on invasive blood tests and requires clinic visits, a time-consuming and potentially nerve-wrecking experience. To render a more continuous picture of stress profile, a non-invasive stress hormone monitoring platform is highly desired.
Here, adapting the original laser-engraved graphene patch with the competitive immunosensing strategy, we developed a highly sensitive, selective, miniaturized mHealth device to non-invasively monitor the level of stress hormones (e.g., cortisol). We report a strong correlation between sweat and circulating cortisol and demonstrate the prompt determination of sweat cortisol variation in response to acute stress stimuli. Moreover, we demonstrate, for the first time, the diurnal cycle and stress-response profile of sweat cortisol, revealing the potential of dynamic stress monitoring enabled by this mHealth sensing system.
Laser-engraved graphene patch for COVID antibody test
The COVID-19 pandemic is an ongoing global challenge for public health systems. Ultrasensitive and early identification of infection is critical in preventing widespread COVID-19 infection by presymptomatic and asymptomatic individuals, especially in the community and in-home settings. Adapting from the laser-engraved patch,
we developed a multiplexed, portable, wireless electrochemical platform for ultra-rapid detection of COVID-19 with immunosensing strategy. It detects viral antigen nucleocapsid protein, IgM and IgG antibodies, as well as the inflammatory biomarker C-reactive protein. The patch offers ultrasensitive, highly selective, and rapid electrochemical detection in the physiologically relevant ranges. We successfully evaluated the applicability of our SARS-CoV-2 RapidPlex platform with COVID19-positive and COVID-19-negative blood and saliva samples. Based on this pilot study, our multiplexed immunosensor platform may allow for high-frequency at-home testing for COVID-19 telemedicine diagnosis and monitoring.
Sweat-powered electronic skin
Existing electronic skin (e-skin) sensing platforms are equipped to monitor physical parameters using power from batteries or near-field communication. For e-skins to be applied in the next generation of robotics and medical devices, they must operate wirelessly and be self-powered. However, despite recent efforts to
harvest energy from the human body, self-powered e-skin with the ability to perform biosensing with Bluetooth communication are limited because of the lack of a continuous energy source and limited power efficiency. We developed a flexible and fully perspiration-powered integrated electronic skin (PPES) for multiplexed metabolic sensing in situ and the fuel is the lactate in sweat. Powered by human sweat in vivo, the patch can selectively monitored key metabolic analytes (e.g., urea, NH4+, glucose, and pH) and the skin temperature during prolonged physical activities and wirelessly transmitted the data to the user interface using Bluetooth. The patch was also able to monitor muscle contraction and work as a human-machine interface for human-prosthesis walking.
Guided microrobotic drug delivery
Synthetic micro/nanomotors have been made to deliver cargo into hard-to-reach regions. However, existing micro/nanomotor platforms cannot display where the micromotors are and
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cannot control the release of cargo in real time in vivo. Collaborating with Lihong Wang's group using photoacoustic computed tomography (PACT), we developed a microrobotic system that could visualize the migration of the micromotor capsules toward targeted regions in intestines and then activate the release of drug at the targeted region, enabling deep imaging and precise control of the micromotors in vivo and promises practical biomedical applications, such as drug delivery.
Human motion powered sweat sensor
As high energy consumption is a crucial challenge in wearable sensing, efficient energy harvesting from human motion represents an attractive approach to sustainably power future
wearables. Despite intensive research activities, most wearable energy harvesters suffer from complex fabrication procedures, poor robustness, and low power density, making them unsuitable for continuous biosensing. We developed a highly robust, mass-producible, and battery-free wearable platform that efficiently extracts power from body motion through a flexible printed circuit board–based freestanding triboelectric nanogenerator. Through seamless system integration and efficient power management, we demonstrated a battery-free triboelectrically driven system that is able to power multiplexed sweat biosensors and wirelessly transmit data to the user interfaces through Bluetooth during on-body human trials.
Low-cost achromatic microscope
Optical systems are typically expected to meet stringent image quality metrics over a broad range of wavelengths. Achromats are the simplest optical components optimized for multispectral performance. Fluorescence
microscopes rely heavily on achromatic designs due to multi-wavelength emission for observation. However, most of the available fluorescence imaging system relied on expensive commercially available achromatic system requiring delicate designs and fabrication. Using dichroic mirrors to replace the conventionally expensive achromatic doublets, we developed a low-cost and compact achromatic system for fluorescence imaging of white blood cells for point-of-care applications. Using this system, a white blood cell count could be achieved to differentiate viral and bacterial infections.
Circadian rhythm for post-harvest vegetable storage
Almost 1/3 of food produced globally is lost or wasted, and yet fewer efforts were devoted to postharvest research and development than to improving productivity. The modular design of plants allows plant tissues and organs to remain biologically active even after harvest; thus,
utilizing the ability of sensing and responding to diverse stimuli could serve as a powerful approach to promote postharvest quality. We investigated whether mimicking aspects of the natural environment predicted to maintain circadian biological rhythms during postharvest storage of green leafy vegetables improves performance and longevity compared to postharvest storage under constant light or constant darkness. Kale, cabbage, green leaf lettuce and spinach were used in the study, and we measured chlorophyll, electrolyte leakage, glucosinolate to assess plant performance. We found that green leafy vegetables improved in several aspects in 12 hr light/12hr dark conditions compared to constant light or constant darkness, and the performance in some aspects could be comparable to refrigeration.