Comparison of signal enhancement strategies for carbamazepine detection in undiluted human saliva using an electrochemical sensor with stencil-printed carbon electrodes.

Carbamazepine (CBZ), a drug prescribed to prevent seizures in people with epilepsy, has a narrow therapeutic range such that patients would greatly benefit from personalized drug dosage recommendations. Saliva is an excellent sample for personalized monitoring of CBZ levels because saliva CBZ concentration correlates with the free concentration of CBZ in blood, and can be collected non-invasively. CBZ level quantification using electrochemical detection has been demonstrated in a variety of electrode systems and samples, however, human saliva presents a particular challenge in terms of its complex composition that can result in signal interference via a high background current at the potentials of interest for CBZ detection. Previous demonstrations of electrochemical detection of CBZ in saliva have included rigorous pre-treatment of the sample using centrifugation and high levels of dilution, which is not compatible with lower-resource field settings for patient monitoring of CBZ levels. In this work, we systematically investigate several strategies to improve the detection of CBZ in a background of undiluted human saliva using polymeric laminate-based devices with stencil-printed carbon electrodes; (i) adding the anionic surfactant sodium dodecyl sulfate to the saliva, (ii) filtering saliva to remove larger molecular weight species, (iii) plasma pretreatment of the device electrodes, and (iv) incubation of the sample on the electrodes. These methods enabled the quantification of therapeutically-relevant concentrations of CBZ in a background of human saliva without the need for saliva preprocessing like dilution.

Rational design and characterization of a lateral flow assay for canine C-reactive protein in wound exudate.

C-reactive protein levels may have clinical value in monitoring different phases of healing and in identifying possible states of infection. As a critical step to further investigate this potential connection, we have demonstrated a lateral flow assay (LFA) for canine CRP level assessment in wound exudate that could be used as a tool in the veterinary clinic setting. In the rational design of our cCRP LFA, we have characterized LFA performance for sequential delivery mode vs. the more common premixed delivery mode using several metrics including dynamic range, sensitivity, limit of detection, and time to result. Although the sequential mode assay results indicated modestly improved signal (3-14%) and limit of detection (in the low ng/mL range for both) for this set of cCRP immunoassay reagents, the premixed mode assay's shorter run time with one less delivery step was chosen for use in this application in which analyte levels are substantially elevated. We have defined a straightforward wound exudate processing procedure that includes centrifugation to extract exudate from canine patient bandages, and subsequent sample dilution for cCRP quantification by our LFA. And, we have demonstrated that our cCRP LFA provides comparable cCRP concentrations to that of gold-standard ELISA performed on the same clinical wound exudate, and serum/plasma samples. Finally, we have highlighted some next steps in the assessment of cCRP as a biomarker for wound healing and infection.

Integrated wax valve for robust fluid control in an electrochemical fabric-based device.

Although fabrics have great promise as substrates for use in wearable precision health applications, there has been relatively little attention focused on the development of control tools suitable for use in fabrics. Fluid control tools in fabric would enable the automation of multi-step sample processing on the device, reducing the need for off-chip sample handling. In this study, we describe the operation and characterization of a wax-based valving method with an integrated resistive heater in fabric for automated fluid delivery. The combination of wax-transfer-printed wax barrier and stencil-printed conductive ink heating element in fabric is a novel approach for achieving fluid control. We demonstrate robust valve operation and a rapid valve response time, and quantify the reproducibility of fluid flow through replicate valves. Further, we characterize wax redistribution in fabric using optical methods and scanning electron microscope imaging. Finally, we demonstrate valve utility in the context of on-device incubation in a fabric-based device for electrochemical glucose sensing. With a fabrication method that is compatible with a variety of substrates, this valving method has broad applicability.

Progress in the development and integration of fluid flow control tools in paper microfluidics.

Paper microfluidics is a rapidly growing subfield of microfluidics in which paper-like porous materials are used to create analytical devices. There is a need for higher performance field-use tests for many application domains including human disease diagnosis, environmental monitoring, and veterinary medicine. A key factor in creating high performance paper-based devices is the ability to manipulate fluid flow within the devices. This critical review is focused on the progress that has been made in (i) the development of fluid flow control tools and (ii) the integration of those tools into paper microfluidic devices. Further, we strive to be comprehensive in our presentation and provide historical context through discussion and performance comparisons, when possible, of both relevant earlier work and recent work. Finally, we discuss the major areas of focus for fluid flow methods development to advance the potential of paper microfluidics for high-performance field applications.

Carbon-Based Solid-State Calcium Ion-Selective Microelectrode and Scanning Electrochemical Microscopy: A Quantitative Study of pH-Dependent Release of Calcium Ions from Bioactive Glass.

Solid-state ion-selective electrodes are used as scanning electrochemical microscope (SECM) probes because of their inherent fast response time and ease of miniaturization. In this study, we report the development of a solid-state, low-poly(vinyl chloride), carbon-based calcium ion-selective microelectrode (Ca(2+)-ISME), 25 µm in diameter, capable of performing an amperometric approach curve and serving as a potentiometric sensor. The Ca(2+)-ISME has a broad linear response range of 5 µM to 200 mM with a near Nernstian slope of 28 mV/log[a(Ca(2+))]. The calculated detection limit for Ca(2+)-ISME is 1 µM. The selectivity coefficients of this Ca(2+)-ISME are log K(Ca(2+),A) = -5.88, -5.54, and -6.31 for Mg(2+), Na(+), and K(+), respectively. We used this new type of Ca(2+)-ISME as an SECM probe to quantitatively map the chemical microenvironment produced by a model substrate, bioactive glass (BAG). In acidic conditions (pH 4.5), BAG was found to increase the calcium ion concentration from 0.7 mM ([Ca(2+)] in artificial saliva) to 1.4 mM at 20 µm above the surface. In addition, a solid-state dual SECM pH probe was used to correlate the release of calcium ions with the change in local pH. Three-dimensional pH and calcium ion distribution mapping were also obtained by using these solid-state probes. The quantitative mapping of pH and Ca(2+) above the BAG elucidates the effectiveness of BAG in neutralizing and releasing calcium ions in acidic conditions.