Guoqing Fu

Flexible pH-Sensing Hydrogel Fibers for Epidermal Applications

Epidermal pH is an indication of the skins physiological condition. For example, pH of wound can be correlated to angiogenesis, protease activity, bacterial infection, etc. Chronic nonhealing wounds are known to have an elevated alkaline environment, while healing process occurs more readily in an acidic environment. Thus, dermal patches capable of continuous pH measurement can be used as point-of-care systems for monitoring skin disorder and the wound healing process. Here, pH-responsive hydrogel fibers are presented that can be used for long-term monitoring of epidermal wound condition. pH-responsive dyes are loaded into mesoporous microparticles and incorporated into hydrogel fibers using a microfluidic spinning system. The fabricated pH-responsive microfibers are flexible and can create conformal contact with skin. The response of pH-sensitive fibers with different compositions and thicknesses are characterized. The suggested technique is scalable and can be used to fabricate hydrogel-based wound dressings with clinically relevant dimensions. Images of the pH-sensing fibers during real-time pH measurement can be captured with a smart phone camera for convenient readout on-site. Through image processing, a quantitative pH map of the hydrogel fibers and the underlying tissue can be extracted. The developed skin dressing can act as a point-of-care device for monitoring the wound healing process.

Broadband wireless radio frequency power telemetry using a metamaterial resonator embedded with non-foster impedance circuitry

Radio Frequency Identification (RFID) and implantable biomedical devices need efficient power and data transfer with very low profile antennas. We propose a low profile electrically small antenna for near-field wireless power and data telemetry employing a metamaterial Split Ring Resonator (SRR) antenna. SRRs can be designed for operation over wide frequencies from RF to visible. However, they are inherently narrowband making them sensitive to component mismatch with respect to external transmit antenna. Here we propose an embedding of a non-foster impedance circuitry into the metamaterial SRR structure that imparts conjugate negative complex impedance to this resonator antenna thereby increasing the effective bandwidth and thus overcoming the fundamental limit for efficient signal coupling. We demonstrate the concept through extensive numerical simulations and a prototype system at the board level using discrete off-the-shelf components and printed circuit SRR antenna at 500 MHz. We show that the power transfer between SRR receive antenna and the external transmit loop antenna is broadened by almost 400 MHz which corresponds to increase in {\Delta}f/fC from 0.49 to 1.65, before and after non-foster circuit activation.

CMOS luminescence lifetime sensor for white LED multi-spectral characterization

Time constants and luminescence lifetimes of an InGaN-based white LED at different wavelengths are characterized by a novel multi-cycle charge modulation based CMOS image sensor chip. To enable high sensitivity, we propose parasitic insensitive multi-cycle charge modulation scheme for low-light lifetime extraction. The designed in-pixel CTIA-based structure is able to capture the weak luminescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated time windows within 10ms, in which each time window has 10us pulse width. A pinned photodiode on chip with 1.04pA dark current is utilized for luminescence detection. The proposed circuitry can achieve 2.1mV/(nW/cm2) responsivity and 4.38nW/cm2 resolution at 630nm wavelength for intensity measurement and 45ns resolution for lifetime measurement.

Disposable colorimetric geometric barcode sensor for food quality monitoring

In this work, we present a disposable paper-based optical sensor arranged as barcode for monitoring food spoilage. The color-changing barcode is embedded in the food packaging and monitored using smart phone. The color change of different optical sensing dyes that make up the barcode is due to the emission of volatile organic compounds (VOCs) from food. Different geometric shapes are assigned to each sensing dye for identification. The sensor fabrication is low-tech and easy to perform. A smart phone quantifies the color change in the barcode food sensor, which provides a non-contact metric of food freshness/spoilage.

CMOS sensor for dual fluorescence intensity and lifetime sensing using multicycle charge modulation

This paper proposes a novel CMOS sensor chip that can realize both fast and accurate intensity and lifetime sensing for fluorescence. To enable high sensitivity, we propose parasitic insensitive multi-cycle charge modulation scheme for low-light lifetime extraction benefiting from simplicity, accuracy and compatibility with CMOS process. The designed in-pixel CTIA-based structure is able to capture the weak fluorescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated time windows within 10ms, in which each time window has 10us pulse width. A pinned photodiode on chip with 1.04pA dark current is utilized for fluorescence detection. The proposed CTIA-based circuitry can achieve 2.1mV/(nW/cm2) responsivity and 4.38nW/cm2 resolution at 630nm for intensity measurement and 45ns resolution for lifetime measurement. We demonstrate functionality by measuring dissolved oxygen concentration with sensitivity of 7.5%/ppm and 6%/ppm in both intensity and lifetime domain.

pH-Sensing Hydrogel Fibers: Flexible pH-Sensing Hydrogel Fibers for Epidermal Applications (Adv. Healthcare Mater. 6/2016)

On page 711 S. Sonkusale, A. Khademhosseini, and co-workers present pH-responsive hydrogel fibers that can be used for long-term monitoring of epidermal wound conditions. pH-responsive dyes are loaded into mesoporous microparticles, which are then embedded into hydrogel fibers developed through microfluidic spinning. The fabricated pH-responsive microfibers are flexible and can create conformal contact with skin. Images of the pH-sensing fibers during real-time pH measurement can be captured with a smart phone camera for convenient readout on-site.

Broadband resonant wireless power transfer using a metamaterial resonator embedded with non-foster impedance circuitry

Wireless and wearable implantable biomedical devices are ushering in a new paradigm in health care and medicine with potential to improve health outcomes at reduced cost and improved quality of life. Magneto-inductive telemetry is widely used for wireless power and data transfer. The typical inductive telemetry core consists of a pair of antenna/coils placed coaxially in space, one inside the device and one placed externally as part of the reader/interrogator. The external coil typically transmits data, which is also harvested for its power and regulated to power up the implant circuitry. One of the most important design criteria is to maximize the coupling between external and implanted coil.

Terahertz metamaterials for modulation and detection

This paper reviews recent work in the area of active metamaterials where transistors and circuitry are embedded within metamaterial structures for novel functions. In one function, embedding of psuedomorphic high electron mobility transistor (pHEMT) within the metamaterial resonator allows realization of a terahertz modulator. A variation of this approach utilizes diodes to modulate the metamaterial response between a perfect absorber and a perfect detector. In another function, a transistor based power detector is embedded within each metamaterial resonator for roomtemperature detection of gigahertz (GHz) radiation. The realized platform has the potential for high resolution imaging at the diffraction limit. These functions indicate range of novel devices enabled through heterogeneous integration of semiconductor devices with metamaterials.