The forefront of metal coating technology for microneedle array electrodes: research and engineering progress on gold plating, platinum plating, and silver plating

1、 Industry background: Micro needle electrodes are reshaping the collection of bioelectric signals

Electrophysiological signals (EMG, ECG, EEG) are the core data sources for health monitoring and clinical diagnosis. The traditional Ag/AgCl wet electrode relies on the conductive gel to reduce the interface impedance, but the gel dehydration leads to impedance drift, unable to achieve long-term stable acquisition; Traditional dry electrodes have high interface impedance and high motion noise. Previous reviews have pointed out that microneedle electrodes are between invasive and non-invasive electrodes, belonging to the category of "microinvasive electrodes". Their microneedle structure can penetrate the stratum corneum and bypass the high impedance introduced by it, significantly improving the quality and accuracy of bioelectric signal recording.

Microneedle Array Electrode (MAE) penetrates the stratum corneum of the skin through microneedles and collects signals in the active epidermal layer. It combines the low impedance of wet electrodes with the non-invasive convenience of dry electrodes and is considered the mainstream solution for the next generation of wearable electrodes.

The decisive variable in the performance of microneedle electrodes is the selection and process of their surface metal coatings - gold (Au), platinum (Pt), and silver (Ag) - which directly determine their conductivity, biocompatibility, electrochemical activity, and long-term stability.

The technical team of Advanced Institute (Shenzhen) Technology Co., Ltd. continues to track the forefront of this field and is now systematically reviewing the technical routes, process comparisons, and application trends of the three major metal coatings.

2、 Technical positioning and core differences of the three major metal coatings

Data source explanationThe bulk conductivity data of silver, gold, and platinum are based on the Materials Science Public Handbook; The conclusions on antibacterial, catalytic and other performance are from multiple peer-reviewed journal reviews (2019-2025).

3、 Comparison of mainstream coating processes

4、 Frontier research progress (2024-2026)

4.1 Gold plated microneedles: from single conductivity to multifunctional platform

The core advantages of gold-plated microneedles are the chemical inertness of gold and the ease of surface functionalization. After thiolation modification, the Au layer can directly immobilize antibodies/aptamers, achieving an integrated design of "electrode as sensor". Multiple reviews from 2024-2025 indicate that electrochemical sensors based on microneedles can achieve biomarker detection by identifying changes in current/voltage/impedance caused by component interactions.

Internal verification by Advanced Institute (Shenzhen) Technology Co., Ltd. shows that after magnetron sputtering gold plating with polymer microneedles, a pure gold nanoparticle film is formed on the surface, which enhances mechanical properties and maintains good original morphology.

4.2 Platinum coated microneedles: the core material for neural regulation

The high charge injection capacity of platinum (CIC>10 mC/cm ²) makes it an important choice for electrical stimulation electrodes.

• Platinum black coating：Scientific ReportsAccording to a report in 2025, platinum black can significantly increase admittance, charge storage capacity, and charge injection capacity, reduce 10 Hz impedance and polarization voltage, and significantly increase the safe distance between electrodes and neurons for stimulation.
• Nano porous platinum (nano Pt)The ACS journal reported that the nano Pt coating remained intact after 5 weeks of in vivo electrical stimulation, withstanding mechanical stress and large charge transfer, and can be mass-produced at the wafer level.

4.3 Silver plated microneedles: the king of conductivity and antibacterial dual function

The silver conductivity is 6.3 × 10 ⁷ S/m (the best among the three), and the Ag ⁺ slow-release antibacterial mechanism significantly inhibits bacterial proliferation on the surface of microneedles. MDPI Review (2025) reports that a microneedle sensor based on platinum wire modified graphene oxide and gold nanoparticles achieves high sensitivity of 14.7 μ A/μ M.

The mainstream solution to silver oxidation problem：

• Ultra thin gold protective layer (5-10 nm) spin coated on Ag surface
• Graphene/Ag composite coating isolates oxidation
• Encapsulated in inert polymer with only exposed needle tip

5、 Advanced Institute (Shenzhen) Technology Co., Ltd. Technical Analysis and Suggestions

VI. Summary

The selection of metal coating for microneedle array electrodes is essentially a four-dimensional trade-off between conductivity, biocompatibility, stability, and cost:

• Pursuing stability and functionality →Au
• Pursuing low impedance and electrical stimulation performance →Pt(Especially nano porous Pt)
• Pursuing ultimate conductivity and antibacterial properties →Ag(Need to cooperate with anti oxidation strategy)

Future trend directionMulti metal composite coating(such as Ti/Pt/Au, Ag/Au core-shell structure) andNanostructured surface(Nanoporous platinum and gold nanowire arrays), meeting multi-dimensional performance requirements simultaneously with a single process.

Advanced Institute (Shenzhen) Technology Co., Ltd. will continue to track the technological evolution in this field and provide full chain technical support to partners from material selection to process implementation based on public literature and proprietary engineering verification.

References

1. Jia L, et al. Sputtered gold-coated polymer microneedles for biosensing.Journal of Biomaterials Science, Polymer Edition, two thousand and twenty-four
2. Zhao T K, et al. Microneedle electrodes for bioelectrical signal acquisition: a review. 2025.
3. Platinum black coated microneedles for neural stimulation.Scientific Reports, two thousand and twenty-five
4. Nanoporous platinum coatings for implantable microelectrodes.ACS Applied Materials & Interfaces, 2025 (early view).
5. Recent advances in microneedle-based electrochemical sensors.MDPI Sensors, two thousand and twenty-five
6. Yuan S M, et al. Scalable manufacturing of metallic microneedles: challenges and opportunities.Chinese Journal of Mechanical Engineering, 2025, 38(1): cover article.

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