Nitrogen-incorporated ultrananocrystalline diamond microneedle arrays for electrochemical biosensing

• ASTM F136 ELI Ti–6Al–4V alloy microneedle arrays were coated with nitrogen-incorporated ultrananocrystalline diamond (N-UNCD).
• N-UNCD coatings were grown on the microneedles using microwave plasma enhanced chemical vapor deposition.
• In vitro electrochemical detection of uric acid and dopamine was shown using unmodified N-UNCD electrodes.

Microneedles are minimally invasive transdermal medical devices that are utilized for various applications, including drug delivery, fluid sampling, micro-dialysis, and electrochemical sensing. These devices are associated with less pain and tissue damage as compared with conventional hypodermic needle-based devices. In this study, we demonstrate fabrication of titanium alloy microneedle arrays with nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) coatings. Microneedles were micromachined from ASTM F136 ELI Ti –6Al–4V alloy, a widely used medical-grade titanium alloy. N-UNCD coatings were deposited on the microneedles using microwave plasma enhanced chemical vapor deposition to enhance mechanical strength, increase hardness, improve biocompatibility, and provide an electrochemically stable surface. The structural and chemical properties of the N-UNCD titanium alloy microneedle arrays were evaluated using scanning electron microscopy and Raman spectroscopy. The mechanical robustness and skin penetration capability of the devices were demonstrated using cadaveric porcine skin. Finally, the electrochemical properties of the N-UNCD electrodes were evaluated; in vitro electrochemical detection of uric acid and dopamine was demonstrated using unmodified N-UNCD electrodes. These results demonstrate the application potential of N-UNCD-coated titanium alloy microneedles for transdermal electrochemical biosensing applications.

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