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This study presents a rapid microfluidic paper-based analytical device (μPAD) capable of simultaneously monitoring Gram-negative bacteria and nitrite ions (NO 2 - ) for water quality monitoring. We utilize gold nanoparticles (AuNPs) functionalized with polymyxin molecules (AuNPs@polymyxin) to cause color change due to aggregation for the detection of Gram-negative bacteria, and antiaggregation in the presence of o -phenylenediamine (OPD) for NO 2 - detection. In this study, Escherichia coli ( E. coli ) serves as the model of a Gram-negative bacterium. Using the developed μPADs, the color changes resulting from aggregation and antiaggregation reactions are measured using a smartphone application. The linear detection ranges from 5.0 × 10 2 to 5.0 × 10 5 CFU/mL ( R 2 = 0.9961) for E. coli and 0.20 to 2.0 μmol/L ( R 2 = 0.995) for NO 2 - . The detection limits were determined as 2.0 × 10 2 CFU/mL for E. coli and 0.18 μmol/L for NO 2 - . Notably, the newly developed assay exhibited high selectivity with no interference from Gram-positive bacteria. Additionally, we obtained acceptable recovery for monitoring E. coli and NO 2 - in drinking water samples with no significant difference between our method and a commercial assay by t test validation. The sensor was also employed for assessing the quality of the pond and environmental water source. Notably, this approach can also be applied to human urine samples with satisfactory accuracy. Furthermore, the assay's stability is extended due to its reliance on AuNPs rather than reagents like antibodies and enzymes, reducing costs and ensuring long-term viability. Our cost-effective μPADs therefore provide a real-time analysis of both contaminants, making them suitable for assessing water quality in resource-limited settings.

In conventional communication systems, dedicated tunable circuit elements are used to realize different functions and achieve performance metrics. For example, tuning the center frequency or the input impedance of an antenna in a radio frequency (RF) system is performed by complex impedance-matching circuits. In this paper, the antenna utilizes the temperature-induced irreversible mechanical deformation of a shape memory alloy (SMA) as a natural way to tune the antenna's shape and configuration, thereby providing inherent tunability without bulky circuit elements. This paradigm of material programming for impedance tuning of an SMA-based antenna is validated by both numerical simulation and measurements., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Deep eutectic solvent (DES) gel electrolytes have recently emerged as promising alternatives to ionic liquid- or water-based gels for "ionic skin" sensor applications. Researchers have also been exploring the effects that varying amounts of water may have on the local hydrogen bonding environment within a few model DES systems. In this study, the physical properties and ionic conductivities of biopolymer (gelatin)-supported gels featuring two established DESs and three DES/water mixture formulations are investigated and compared. The DES/water mixtures are formed by combining choline chloride with one of three organic hydrogen bond donors (HBDs), ethylene glycol, glycerol, or 1,2-propanediol, in a 1:2 molar ratio, together with a controlled amount of water, 25 mol % (approximately 5-6 wt % water). For the same fixed gelatin content (20 wt %), DES/water mixture gel Young's modulus values are found to be tunable based on the organic HBD identity, increasing 6-fold from 7 (1,2-propanediol) to 42 (glycerol) kPa. Furthermore, large differences are observed in the resulting gel properties when water has been intentionally added to well-studied DESs. Coformulation with water is found to increase ethylene glycol-based DES gel toughness, measured via tensile testing, from 23 to 68 kJ/m 3 while simultaneously boosting gel room temperature ionic conductivity from 3.3 to 5.2 mS/cm. These results highlight the multiple roles that controlled amounts of water in DES can play within gelatin-supported DES/mixture gel electrolytes, such as influencing gelatin self-assembly and reducing local viscosity to promote facile ion transport.

Physically intimate, real-time monitoring of human biomarkers is becoming increasingly important to modern medicine and patient wellness. Such monitoring is possible due to advances in soft and flexible materials, devices and bioelectronics systems. Compared to other flexible platforms, multifilament textile fibers or threads offer superior flexibility, material diversity, and simple ambient processing to realize a wide range of flexible devices such as sensors, electronics, and microfluidics. In this paper, we realize unique flexible transistors on threads and interconnect them to realize logic gates and small-scale integrated circuits. Compared to prior textile-based transistors, the proposed thread-based transistors (TBTs) are realized with a readily shaped, colloidally dispersed gel consisting of silica nanoparticles and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) ionic liquid for all-around electrolyte gating of a carbon nanotube (CNT) semiconducting network assembled on the thread. We interconnect TBTs with thread-based electrochemical sensors (TBEs) to realize an all-thread based multiplexed diagnostic device. All-thread based platforms are thin, highly flexible and conformal, allowing them to be worn directly on the skin without any polymeric substrate, or sutured transdermally using a needle.

A fabrication method for a stable entrapment of optically responsive dyes on a thread substrate is proposed to move towards a detection system that can be integrated into clothing. We use the dyes 5,10,15,20-Tetraphenyl-21H,23H-porphine manganese(III) chloride (MnTPP), methyl red (MR), and bromothymol blue (BTB), for a proof-of-concept. Our optical approach utilizes a smartphone to extract and track changes in the red (R), green (G) and blue (B) channel of the acquired images of the thread to detect the presence of an analyte. We demonstrate sensing of 50-1000 ppm of vapors of ammonia and hydrogen chloride, components commonly found in cleaning supplies, fertilizer, and the production of materials, as well as dissolved gas sensing of ammonia. The devices are shown to be stable over time and with agitation in a centrifuge. This is attributed to the unique dual step fabrication process that entraps the dye in a stable manner. The facile fabrication of colorimetric gas sensing washable threads is ideal for the next generation of smart textile and intelligent clothing.

In this work, a paper-based optoelectronic sensor (paper-nose) is presented for sensing volatile gases in air. The proposed optoelectronic sensor is a combination of both colorimetric (optical) and chemiresistive (electronic) sensor arrays in order to improve the selectivity of the paper-nose in the complex air background. The optical sensors are based on chemoresponsive dyes, namely Reichardt's dye (2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate), bromocresol purple, methyl red, bromothymol blue, brilliant yellow and manganese tetraphenylporphyrin (Mn-TPP). The chemiresistive sensors are based on nanomaterials, such as carbon nanotubes (CNT), PEDOT:PSS, graphite, and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI). Sensor is fabricated through direct handwriting of sensing materials using a pen on paper without the need of expensive cleanroom facilities. The optoelectronic sensor is tested in ambient air with different volatile gases such as methanol, ammonia, toluene, acetone and ethanol and their mixtures of varying concentrations. The detected electrical and optical responses together form a unique signature for each volatile gas and its mixture. Support-vector machine (SVM) is applied for target classification and detection. From the SVM result, it is found that better discriminative power is achieved by combining optical and electrical responses., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Chronic wounds are a major health concern and they affect the lives of more than 25 million people in the United States. They are susceptible to infection and are the leading cause of nontraumatic limb amputations worldwide. The wound environment is dynamic, but their healing rate can be enhanced by administration of therapies at the right time. This approach requires real-time monitoring of the wound environment with on-demand drug delivery in a closed-loop manner. In this paper, a smart and automated flexible wound dressing with temperature and pH sensors integrated onto flexible bandages that monitor wound status in real-time to address this unmet medical need is presented. Moreover, a stimuli-responsive drug releasing system comprising of a hydrogel loaded with thermo-responsive drug carriers and an electronically controlled flexible heater is also integrated into the wound dressing to release the drugs on-demand. The dressing is equipped with a microcontroller to process the data measured by the sensors and to program the drug release protocol for individualized treatment. This flexible smart wound dressing has the potential to significantly impact the treatment of chronic wounds., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Luminescence plays an important role in many scientific and industrial applications. This paper proposes a novel complementary metal-oxide-semiconductor (CMOS) sensor chip that can realize both luminescence intensity and lifetime sensing. To enable high sensitivity, we propose parasitic insensitive multicycle charge modulation scheme for low-light lifetime extraction benefiting from simplicity, accuracy, and compatibility with deeply scaled CMOS process. The designed in-pixel capacitive transimpedance amplifier (CTIA) based structure is able to capture the weak luminescence-induced voltage signal by accumulating photon-generated charges in 25 discrete gated 10-ms time windows and 10-μs pulsewidth. A pinned photodiode on chip with 1.04 pA dark current is utilized for luminescence detection. The proposed CTIA-based circuitry can achieve 2.1-mV/(nW/cm 2 ) responsivity and 4.38-nW/cm 2 resolution at 630 nm wavelength for intensity measurement and 45-ns resolution for lifetime measurement. The sensor chip is employed for measuring time constants and luminescence lifetimes of an InGaN-based white light-emitting diode at different wavelengths. In addition, we demonstrate accurate measurement of the lifetime of an oxygen sensitive chromophore with sensitivity to oxygen concentration of 7.5%/ppm and 6%/ppm in both intensity and lifetime domain. This CMOS-enabled oxygen sensor was then employed to test water quality from different sources (tap water, lakes, and rivers).

In this work, pH sensing directly in biological media using three dimensional liquid gated graphene transistors is presented. The sensor is made of suspended network of graphene coated all around with thin layer of hafnium oxide (HfO2), showing high sensitivity and sensing beyond the Debye-screening limit. The performance of the pH sensor is validated by measuring the pH of isotonic buffered, Dulbecco's phosphate buffered saline (DPBS) solution, and of blood serum derived from Sprague-Dawley rat. The pH sensor shows high sensitivity of 71 ± 7 mV/pH even in high ionic strength media with molarities as high as 289 ± 1 mM. High sensitivity of this device is owing to suspension of three dimensional graphene in electrolyte which provides all around liquid gating of graphene, leading to higher electrostatic coupling efficiency of electrolyte to the channel and higher gating control of transistor channel by ions in the electrolyte. Coating graphene with hafnium oxide film (HfO2) provides binding sites for hydrogen ions, which results in higher sensitivity and sensing beyond the Debye-screening limit. The 3D graphene transistor offers the possibility of real-time pH measurement in biological media without the need for desaltation or sample preparation., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this paper, we present a three-dimensional graphene foam made of few layers of CVD grown graphene as a scaffold for growing cardiac cells and recording their electrical activity. Our results show that graphene foam not only provides an excellent extra-cellular matrix (ECM) for the culture of such electrogenic cells but also enables recording of its extracellular electrical activity in-situ. Recording is possible due to graphene's excellent conductivity. In this paper, we present our results on the fabrication of the graphene scaffold and initial studies on the culture of cardiac cell lines such as HL-1 and recording of their real-time electrical activity.

Threads, traditionally used in the apparel industry, have recently emerged as a promising material for the creation of tissue constructs and biomedical implants for organ replacement and repair. The wicking property and flexibility of threads also make them promising candidates for the creation of three-dimensional (3D) microfluidic circuits. In this paper, we report on thread-based microfluidic networks that interface intimately with biological tissues in three dimensions. We have also developed a suite of physical and chemical sensors integrated with microfluidic networks to monitor physiochemical tissue properties, all made from thread, for direct integration with tissues toward the realization of a thread-based diagnostic device (TDD) platform. The physical and chemical sensors are fabricated from nanomaterial-infused conductive threads and are connected to electronic circuitry using thread-based flexible interconnects for readout, signal conditioning, and wireless transmission. To demonstrate the suite of integrated sensors, we utilized TDD platforms to measure strain, as well as gastric and subcutaneous pH in vitro and in vivo ., Competing Interests: The authors declare no conflict of interest.

Current methods in treating chronic wounds have had limited success in large part due to the open loop nature of the treatment. We have created a localized 3D-printed smart wound dressing platform that will allow for real-time data acquisition of oxygen concentration, which is an important indicator of wound healing. This will serve as the first leg of a feedback loop for a fully optimized treatment mechanism tailored to the individual patient. A flexible oxygen sensor was designed and fabricated with high sensitivity and linear current output. With a series of off-the-shelf electronic components including a programmable-gain analog front-end, a microcontroller and wireless radio, an integrated electronic system with data readout and wireless transmission capabilities was assembled in a compact package. Using an elastomeric material, a bandage with exceptional flexibility and tensile strength was 3D-printed. The bandage contains cavities for both the oxygen sensor and the electronic systems, with contacts interfacing the two systems. Our integrated, flexible platform is the first step toward providing a self-operating, highly optimized remote therapy for chronic wounds.

Paper, a cheap and ubiquitous material, has great potential to be used as low-cost, portable and biodegradable platform for chemical and biological sensing application. In this paper, we are exploring a low-cost, flexible and reliable method to effectively pattern paper for capturing optical dyes and for flow-based delivery of target samples for colorimetric chemical sensing. In this paper, we target the detection of ammonia (NH3) and carbon dioxide (CO2), two of the important environmental and health biomarkers. By functionalizing the paper platform with diverse cross-reactive dyes sensitive to NH3 and CO2, their selective sensing within a certain pH range, as well as their detection at different concentrations can be achieved. The images of paper based device were captured by a flatbed scanner and processed in MATLAB(®) using a RGB model and PCA for quantitative analysis. Paper based devices with readout using ubiquitous consumer electronic devices (e.g. smartphones, flatbed scanner) are considered promising approaches for disease screening in developing countries with limited resources., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We present a microfluidic optoelectronic sensor for saliva diagnostics with a potential application for non-invasive early diagnosis of stomach cancer. Stomach cancer is the second most common cause of cancer-related deaths in the world. The primary identified cause is infection by a gram-negative bacterium Helicobacter pylori. These bacteria secrete the enzyme urease that converts urea into carbon dioxide (CO2) and ammonia (NH3), leading to their elevated levels in breath and body fluids. The proposed optoelectronic sensor will detect clinically relevant levels of CO2 and NH3 in saliva that can potentially be used for early diagnosis of stomach cancer. The sensor is composed of the embedded in a microfluidic device array of microwells filled with ion-exchange polymer microbeads doped with various organic dyes. The optical response of this unique highly diverse sensor is monitored over a broad spectrum, which provides a platform for cross-reactive sensitivity and allows detection of CO2 and NH3 in saliva at ppm levels., (Copyright © 2014 Elsevier B.V. All rights reserved.)

We present a portable lab-on-chip device for high-throughput trapping and lysis of single cells with in-situ impedance monitoring in an all-electronic approach. The lab-on-chip device consists of microwell arrays between transparent conducting electrodes within a microfluidic channel to deliver and extract cells using alternating current (AC) dielectrophoresis. Cells are lysed with high efficiency using direct current (DC) electric fields between the electrodes. Results are presented for trapping and lysis of human red blood cells. Impedance spectroscopy is used to estimate the percentage of filled wells with cells and to monitor lysis. The results show impedance between electrodes decreases with increase in the percentage of filled wells with cells and drops to a minimum after lysis. Impedance monitoring provides a reasonably accurate measurement of cell trapping and lysis. Utilizing an all-electronic approach eliminates the need for bulky optical components and cameras for monitoring., (© 2013 Published by Elsevier B.V.)

This paper illustrates an architectural design of a novel variable input-feature correlated asynchronous sampling and time-encoded digitization approach for source compression and direct feature extraction from physiological signals. The complete architecture represents an analog-to-information (A2I) converter, designed for ultra-low-power mixed-signal very-large-scale integrated implementation. The device will be suitable for long-term wearable monitoring of physiological signals, such as electrocardiogram (ECG). We show representative case studies on QRS detection in an ECG signal utilizing the proposed A2I converter to prove the functionality of the design. Simulation results show large source compression in the ECG signal and more than 98% efficiency in the detection of the Q, R, and S waves for challenging ECG waveforms, all with extremely low-power and storage requirements.