(Invited) integration of Microneedles and Electrochemical Sensors for Medical Applications
Authors: Narayan Roger 
Published: September 2023

Microneedles are small-scale devices that may be used for access to interstitial fluid and/or capillary blood for transdermal monitoring of chemicals [1]. In this presentation, the integration of several types of electrochemical sensors with hollow microneedles will be considered. For example, carbon fiber electrodes have been integrated with digital micromirror device-produced microneedles; ascorbic acid and hydrogen peroxide were detected with these devices [2]. Carbon paste electrodes have also been integrated with digital micromirror device-produced microneedles; electrodes made from rhodium-dispersed carbon paste were used for hydrogen peroxide sensing [3]. In addition, lactate oxidase-modified rhodium-dispersed carbon paste electrodes were demonstrated for lactate sensing, including in the presence of interferents such as ascorbic acid, uric acid, and acetaminophen. A multiplexed microneedle array containing digital micromirror device-produced microneedles was subsequently used for amperometric detection of glucose, lactate, and pH; detection of these analytes in complex media was shown [4]. More recently, digital micromirror device-produced hollow microneedles were modified with a working sensor, which was prepared with graphene ink and 4 (3-Butyl-1-imidazolio)-1-butanesulfonate) ionic liquid. Direct oxidation of fentanyl via square-wave voltammetry was shown; a detection limit of 27.8 μM was demonstrated using this approach [5]. Two photon polymerization has also been used to create hollow microneedles for biosensing; a porous carbon electrode created using interference lithography was used for potassium ion sensing in the presence of interfering sodium ions [6]. In another study, nitrogen-incorporated ultrananocrystalline diamond coatings were deposited on Ti –6Al–4V alloy microneedles using microwave plasma enhanced chemical vapor deposition; dopamine and uric acid were electrochemically detected in an in vitro study [7]. These studies indicate that microneedles may have utility for minimally invasive detection of analytes in a real time manner. Benefits and disadvantages of the microneedle-based sensing approach as well as efforts needed for clinical translation of microneedle-based sensing technology will be considered.
References
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[4] Miller PR, Skoog SA, Edwards TL, Lopez DM, Wheeler DR, Arango DC, Xiao X, Brozik SM, Wang J, Polsky R, Narayan RJ. Multiplexed microneedle-based biosensor array for characterization of metabolic acidosis. Talanta. 2012;88:739–742.
[5] Joshi P, Riley PR, Mishra R, Azizi Machekposhti S, Narayan R. Transdermal polymeric microneedle sensing platform for fentanyl detection in biofluid. Biosensors. 2022 Mar 27;12:198.
[6] Miller PR, Xiao X, Brener I, Burckel DB, Narayan R, Polsky R. Microneedle-based transdermal sensor for on-chip potentiometric determination of K+. Advanced Healthcare Materials. 2014;3:876-881.
[7] Skoog SA, Miller PR, Boehn RD, Sumant AV, Polsky R, Narayan RJ. Nitrogen-incorporated ultrananocrystalline diamond microneedle arrays for electrochemical biosensing. Diamond and Related Materials. 2015;54:39-46.