An Accessible Yarn-Based Sensor for In-Field Detection of Succinylcholine Poisoning

LiFT (a Lithium Fiber-Based Test): An At-Home Companion Diagnostics for a Safer Lithium Therapy in Bipolar Disorder

This work presents LiFT (a lithium fiber-based test), a low-cost electrochemical sensor that can measure lithium in human saliva and urine with FDA-required accuracy. Lithium is used for the treatment of bipolar disorder, and has a narrow therapeutic window. Close monitoring of lithium concentration in biofluids and adjustment of drug dosage can minimize the devastating side effects. LiFT is an inexpensive, yet accurate and simple-to-operate lithium sensor for frequent at-home testing for early identification of lithium toxicity. The low cost and high accuracy of LiFT are enabled through an innovative design and the use of ubiquitous materials such as yarn and carbon black for fabrication. LiFT measures Li+ through potentiometric recognition using a lithium selective sensing membrane that is deposited on the ink-coated yarn. A detection limit of 0.97 µM is obtained with a sensitivity of 59.07±1.25 mV/decade for the Li+ sensor in deionized water. Moreover, the sodium correction extended LiFT's linear range in urine and saliva to 0.5 mM. The LiFT platform sends the test results to the patient's smartphone, which subsequently can be shared with the patient's healthcare provider to expedite diagnosis and prevention of acute lithium toxicity.

Toward Personalized Treatment of Depression: An Affordable Citalopram Test based on a Solid-Contact Potentiometric Electrode for at-Home Monitoring of the Antidepressant Dosage

Citalopram (CTLP) is one of the most common antidepressants prescribed worldwide. It has a narrow therapeutic window and can cause severe toxicity and mortality if the dosage exceeds the safe level. Reports indicated that at-home monitoring of citalopram dosage considerably benefits the patients, yet there are no devices capable of such measurement of citalopram in biofluids. This work presents an affordable citalopram test for at-home and point-of-care monitoring of citalopram levels in urine, ensuring a safe and effective drug compliance. Our platform consists of a citalopram-selective yarn-based electrode (CTLP-SYE) that uses polymeric sensing membranes to provide valuable information about drug concentration in urine. CTLP-SYE is noninvasive and has a response time of fewer than 10 s. The fabricated electrode showed near-Nernstian behavior with a 52.3 mV/decade slope in citalopram hydrobromide solutions ranging from 0.5 μM to 1.0 mM, with a detection limit of 0.2 μM. Results also indicated that neither interfering ions nor pH affects electrode performance. We showed that CTLP-SYE could accurately and reproducibly measure citalopram in human urine (RSD 2.0 to 3.2%, error <12%) at clinically relevant concentrations. This work paves the way for the personalized treatment of depression and accessible companion diagnostics to improve treatment efficacy and safety.

FAST (Flexible Acetylcholine Sensing Thread): Real-Time Detection of Acetylcholine with a Flexible Solid-Contact Potentiometric Sensor

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.