Sustainable agricultural practices are vital to meet the needs of a rapidly growing global demand for food. Monitoring plant health is crucial for enhancing crop yields. Salicylic acid (SA) is a plant hormone that plays a key role in the defense mechanisms plants employ against various stress factors. Changes in SA levels serve as an indicator that a plant is experiencing stress. Here, we present a low-cost electrochemical sensor fabricated using porous laser-induced graphene material for the measurement of plant stress. It employs square wave voltammetry to monitor SA levels using a wireless potentiostat. The sensor shows a high sensitivity of 144.28 μA mM⁻¹ to SA, with a linear detection range of 6.6 μM to 200 μM and a limit of detection of 1.44 μM. The surface of the working electrode was modified with Nafion to enable continuous in situ stress monitoring. The sensor's practicality has been demonstrated through real-time stress monitoring in aloe vera and philodendron hederaceum plant species.

Acetylcholine (ACh) is involved in memory and learning and has implications in neurodegenerative diseases; it is therefore important to study the dynamics of ACh in the brain. This work creates a flexible solid-contact potentiometric sensor for in vitro and in vivo recording of ACh in the brain and tissue homogenate. We fabricate this sensor using a 250 μm diameter cotton yarn coated with a flexible conductive ink and an ACh sensing membrane that contains a calix[4]arene ionophore. The exposed ion-to-electron transducer was sealed with a 2.5 μm thick Parylene C coating to maintain the flexibility of the sensor. The resulting diameter of the flexible ACh sensing thread (FAST) was 400 μm. The FAST showed a linear response range from 1.0 μM to 10.0 mM in deionized water, with a near-Nernstian slope of 56.11 mV/decade and a limit of detection of 2.6 μM. In artificial cerebrospinal fluid, the limit of detection increased to 20 μM due to the background signal of ionic content of the cerebrospinal fluid. The FAST showed a signal stability of 226 μV/h over 24 h. We show that FAST can measure ACh dynamics in sheep brain tissue and sheep brain homogenate after ACh spiking. FAST is the first flexible electrochemical sensor for monitoring ACh dynamics in the brain.

The COVID-19 pandemic revealed a pressing need for the development of sensitive and low-cost point-of-care sensors for disease diagnosis. The current standard of care for COVID-19 is quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). This method is sensitive, but takes time, effort, and requires specialized equipment and reagents to be performed correctly. This make it unsuitable for widespread, rapid testing and causes poor individual and policy decision-making. Rapid antigen tests (RATs) are a widely used alternative that provide results quickly but have low sensitivity and are prone to false negatives, particularly in cases with lower viral burden. Electrochemical sensors have shown much promise in filling this technology gap, and impedance spectroscopy specifically has exciting potential in rapid screening of COVID-19. Due to the data-rich nature of impedance measurements performed at different frequencies, this method lends itself to machine-leaning (ML) algorithms for further data processing. This review summarizes the current state of impedance spectroscopy-based point-of-care sensors for the detection of the SARS-CoV-2 virus. This article also suggests future directions to address the technology’s current limitations to move forward in this current pandemic and prepare for future outbreaks.

Saliva has emerged as a primary biofluid for non-invasive disease diagnostics. Saliva collection involves using kits where individuals stimulate saliva production via a chewing device like a straw, then deposit the saliva into a designated collection tube. This process may pose discomfort to patients due to the necessity of producing large volumes of saliva and transferring it to the collection vessel. This work has developed a saliva collection and analysis device where the patient operates it like a lollipop, stimulating saliva production. The lollipop-mimic device contains yarn-based microfluidic channels that sample saliva and transfer it to the sensing zone embedded in the stem of the device. We have embedded electrochemical sensors in the lollipop platform to measure vanillin levels in saliva. Vanillin is the most common food flavoring additive and is added to most desserts such as ice cream, cakes, and cookies. Overconsumption of vanillin can cause side effects such as muscle weakness, and damage to the liver, kidneys, stomach, and lungs. We detected vanillin using direct oxidation at a laser-induced graphene (LIG) electrode. We showed a dynamic range of 2.5 μM to 30 μM, covering the physiologically relevant concentration of vanillin in saliva. The lab-on-a-lollipop platform requires only 200 μL of saliva and less than 2 minutes to fill the channels and complete the measurement. This work introduces the first sensor-embedded lollipop-mimic saliva collection and measurement system.

Muscle on a Chip devices are valuable research tools for interrogating the structure and physiology of engineered heart, skeletal, or smooth muscle tissue constructs from the molecular to the multi‐cellular level. However, many existing devices rely on functional assays with limited throughput, such as optical microscopy, to measure contractility. Although electrical components have been integrated to automate recordings in advanced devices, their fabrication typically requires specialized equipment found in cleanroom facilities. In this work, miniature strain gauges are engineered to record the contractions of engineered skeletal muscle bundles using only benchtop fabrication equipment. A commercial CO₂ laser is employed to generate patterns of laser‐induced graphene (LIG) on polyimide (PI) films. LIG is then transferred from PI to thin polydimethylsiloxane (PDMS) films to make conductive and intrinsically flexible and stretchable layers that demonstrate long‐term stability under repeated cycles of stretch. Engineered skeletal muscle bundles are anchored to LIG‐PDMS strain gauges and their contraction is sensed in response to electrical stimulation, which is delivered by LIG‐PI stimulation electrodes also integrated into the device. Collectively, these results demonstrate that LIG is an attractive material for rapidly and inexpensively integrating electrical components for in situ strain sensing and electrical stimulation in Muscle on a Chip devices.