Citation: Liao, Z.; Zhou, Q.; Gao, B.
Electrochemical Microneedles:
Innovative Instruments in Health
Care. Biosensors 2022, 12, 801.
https://doi.org/10.3390/
bios12100801
Received: 28 August 2022
Accepted: 24 September 2022
Published: 28 September 2022
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Review
Electrochemical Microneedles: Innovative Instruments in
Health Care
Zhijun Liao, Qian Zhou and Bingbing Gao *
School of Pharmaceutical Sciences, Nanjing Tech University, Nanjing 211816, China
* Correspondence: gaobb@njtech.edu.cn
Abstract:
As a significant part of drug therapy, the mode of drug transport has attracted worldwide
attention. Efficient drug delivery methods not only markedly improve the drug absorption rate,
but also reduce the risk of infection. Recently, microneedles have combined the advantages of
subcutaneous injection administration and transdermal patch administration, which is not only
painless, but also has high drug absorption efficiency. In addition, microneedle-based electrochemical
sensors have unique capabilities for continuous health state monitoring, playing a crucial role in
the real-time monitoring of various patient physiological indicators. Therefore, they are commonly
applied in both laboratories and hospitals. There are a variety of reports regarding electrochemical
microneedles; however, the comprehensive introduction of new electrochemical microneedles is still
rare. Herein, significant work on electrochemical microneedles over the past two years is summarized,
and the main challenges faced by electrochemical microneedles and future development directions
are proposed.
Keywords: electrochemical; real-time monitoring; biosensor; fabrication method; microneedle
1. Introduction
Electrochemistry is a science that studies the charged interface phenomenon formed
by two kinds of conductors and its changes [
1
]. Due to its high sensitivity [
2
], ease of
use, rapid response, economy, and mobile advantages, electrochemistry is widely used in
wearable electronic equipment [
3
], clinical application of activated coating time (ACT) [
4
],
sewage treatment, etc. At the same time, it also has some shortcomings, including the need
for large-scale instruments, inconvenience, poor long-term sensitivity, and physiological
indicators that often need to be tested
in vitro
. In addition, Heubner et al. [
5
] wrote that
there were some shortcomings in the use of a 2-electrode half-cell system for the testing of
electrochemical performance (such as the continuous decline in the potential stability of
the working electrode and cross-talk phenomena). Thus, it is often used in combination
with other techniques, such as liquid chromatography, microneedles, and photochemistry.
Microneedle administration can prevent the liver first-pass effect and enzyme reac-
tion damage in the gastrointestinal tract during the oral administration of drugs, thereby
doubling drug absorption and utilization rates [
6
]. The action mode is to punch out a large
number of fine pipelines by stimulating the skin and then directly injecting the drugs into
the dermis layer and deep subcutaneous tissue so that the active ingredients can penetrate
into the skin. According to the difference in drug release mechanisms [
7
], microneedles
can be divided into five categories: solid microneedles [
8
], hollow microneedles [
9
], coated
microneedles [
10
], soluble microneedles, and hydrogel microneedles [
11
]. Each type has
different advantageous features, e.g., hollow microneedles can be monitored in real time
using built-in electrodes, and soluble microneedles can be rapidly degraded by skin tissue
fluid after penetrating into the skin, thus releasing the drugs from the needle body. More-
over, microneedles have the following advantages: painless, noninvasive, macromolecular
penetration into the stratum corneum [
12
], controllable dose, and high bioavailability [
13
].
Biosensors 2022, 12, 801. https://doi.org/10.3390/bios12100801 https://www.mdpi.com/journal/biosensors
