Microneedle-Integrated Device for Transdermal Sampling and Analyses of Targeted Biomarkers

Abstract

Currently available point-of-care systems for body fluid collection exhibit poor integration with sensors. Herein, the design of a disposable device for interstitial fluid (ISF) extraction as well as glucose, lactate, and potassium ion (K⁺) monitoring is reported on. It is minimally invasive and appropriate for single use, minimizing the risk of infection to the user. This microscale device contains a 3D-printed cap-like structure with a four-by-four microneedle (MN) array, bioreceptor-modified carbon fiber (CF)-sensing surface, and negative pressure convection technology. These features are incorporated within a compact, self-contained, and manually operated microscale device, which is capable of withdrawing ≈3.0 μL of ISF from the skin. MN arrays applied with an upward driving force may increase the ISF flow rate. Moreover, functionalized CF working electrodes (WE₁, WE₂, WE₃) are shown to selectively detect lactate, glucose, and K⁺ with high sensitivities of 0.258, 0.549, and 0.657 μA μm ^-1 cm^-2 and low detection limits of 0.01, 0.080, 0.05 μm, respectively. Ex vivo testing on porcine skin is used to detect the ISF levels of the biomarkers. The microscale device can be a replacement for current point-of-care diagnostic approaches.

Keywords: 3D printing; diffusion; glucose monitoring; interstitial fluids; microneedle arrays; transdermal.

Figure 1

Schematic illustration of CF WEs fabrication. A) Sonication treatment and functionalization of CFs with LO _x , GO _x , and AOCE‐6 to make WE₁, WE_2, and WE₃, B) Attachment of CFs with copper foil using silver epoxy resin, and C) preparation of electrolyte gel as well as assembly of three WEs into gel slab and device. Symbols were defined as: CFs, carbon fibers; HCl, hydrochloric acid; HAuCl₄, tetrachloroauric acid; APTMS, 3‐aminopropyl trimethyl siloxane; HCHO, formaldehyde; Pd(acac)_2, palladium acetylacetonate; EETMS, 2 ‐(3.4 epoxycyclohexyl) ethyltrimethoxy silane; LO _x , lactate oxidase; GO _x , glucose oxidase; CE, crown ether; Wes, working electrodes; Fe [(CN)₆]^3−/4−, potassium ferricyanide.

Figure 2

Schematic illustration of MN array preparation and microscale device assembly. A) DLP 3D printing of MN cap. B) Alignment of all of the components of microscale device. Symbols are defined as follows: 3D DLP, 3D digital light projection; MN, microneedle; and PDMS, polydimethylsiloxane.

Figure 3

Optical images of MN arrays on a) square plate and b) cap . SEM micrographs of c) MN array, d) MN tip, and e) MN oblique view. Keyence laser scanning optical microscopy 3D image of the f) MN and g) dimensions of the MNs shown by the plot between height (y‐axis) and width of the needle (x‐axis). Optical images of trypan blue‐coated punctured porcine skin using MN arrays of height h) 750 μm, i) 800 μm, j) 900 μm, and k) 950 μm.

Figure 4

SEM images of: a) unmodified CF; b) CF/APTMS/Pd@Au/LO _x , c) CF/APTMS/Pd@Au/GO _x , d) CF/APTMS/Pd@Au/AOCE‐6, e–f) electrolyte gel slab, g) SEM–EDS elemental mapping of the elements 1) C, 2) Si, 3) Cl, 4) O, 5) Au, and (6) Pd, h) area EDS spectrum. Inset pictures i–iii) magnified views highlighting the coating on CF surfaces.

Figure 5

XPS C1s spectra of a) unmodified CF, b) modified CF/APTMS/Pd@Au/AOCE‐6, and c) CF/APTMS/Pd@Au/enzyme. FTIR profile of d) CF WEs and e) magnified region of Figure (d). Legends 1–4 represent CF/APTMS and CF WEs (WE₁, WE₂, WE₃).

Figure 6

Fluid collection profile obtained from pig skin ex vivo after different durations.

Figure 7

Electrochemical characterization of CF WEs before and after stepwise modification. CV plots for a) CF/APTMS/Pd@Au/LO _x , b) CF/APTMS/Pd@Au/GO _x , and c) CF/APTMS/ Pd@Au/AOCE‐6 electrodes recorded in semisolid electrolyte gel slab. Legends 1–3 represent the voltammograms after each functionalization. Legend 4 in Figure (c) was obtained after adding KCl solution.

Figure 8

Amperometric responses of a,d) APTMS/Pd@Au/LO _x , b,e) APTMS/Pd@Au/GO _x , and c) APTMS/Pd@Au/AOCE‐6‐coated CFs. Inset pictures show the corresponding calibration curves of current responses versus concentration of analytes, i) enzyme kinetics for LO _x /GO _x by the Michaelis–Menten model. f) is the exponential decay curve model for potassium ion detection.

Figure 9

Ex vivo testing of the device on porcine skin. Optical images of a) applying the device on skin for insertion and collection of ISF, and b) three‐electrode system for transdermal monitoring of analytes. CV plots for measuring ISF: a) glucose, b) lactate, c) potassium ion levels. Legend 1 in Figure (c–e) represents the introduction of analytes.

Figure 10

a) Schematic design of the simulated electroactive space in electrolyte, b) 2D domain of the microsensor electrode radius (r _e), and c) color maps showing the expansion of the diffusion layer over time (0–200 s).