(Digital Presentation) Micro-Surface Engineering of Integrated Silicon Microtechnologies for the Development of Sensing and Biosensing Platforms
Authors: Juska Vuslat B. , O'Riordan Alan 
Published: November 2022

Microfabrication techniques used in semiconductor industry deliver high yield of devices and silicon microtechnologies undoubtedly have a reputation of a well-established platform for manufacture. A Silicon-wafer is the most commonly used substrate due to its low-cost; therefore for decades several protocols have been developed in order to process this particular material for micro-nano electronics. Today, it is possible to manufacture ultramicro-nano scale devices with multiple steps of lithography, deposition, and lift-off. Clearly, such progress of microsystems has been one of the major interests of biology-based research fields due to the need for small-reproducible devices with appropriate interface features, in particular for biosensing-applications.
Biosensing technologies have an important contribution to a daily basis life with the examples of glucometers, pregnancy tests, Covid-19 tests, etc. Microtechnologies combined with sensing systems are clearly a rising-star due to several benefits of microfabrication protocols such as excellent reproducibility, miniaturization capabilities, low-cost and design flexibility for device fabrication.
Establishment of a successful fabrication route of ultramicro devices with high reproducibility is a challenge. Figure1 shows an example fabrication-flow of one of our devices. We have developed several successful fabrication flows for device manufacturing and we have developed several designs of gold chips based on band-electrode-array[1], disk-electrode-array[2], and multiplexing[3] for varying (bio)sensing applications. Figure2 shows a series of SEM images of designed, fabricated and foam-modified devices.
One of the significant key of using such tiny devices is the electrochemical reproducibility of the gold surfaces to establish a successful sensing platform. Therefore we assessed the effect of several cleaning protocols on the electrochemical characteristics of ultramicro-electrode-devices. As an example, Figure3a shows one of the 6-sensing-electrodes on a multiplexed-device(1µm-width,45µm-length). After the cleaning protocol of chip, we studied cyclic voltammetry in a redox probe(5mM Fe(CN)6
3–/4– in 1M KCl). Clearly, applied protocol provides reproducible redox-active sensing-electrode surfaces therefore; we obtained overlapping voltammograms of 6-electrode-on-chip(Figure3b). We also investigated the surface morphology of the gold surface(Figure3c). We discovered that the cleaning protocol increases surface-roughness which may lead a redox-active surface.
One another key aspect of our study is the application of these tiny devices. We in particular studied miniaturization of hydrogen-bubble template with chips to explore scaling-down limits of in situ template. Figure2 represents many of designs applied with in situ template studied in highly acidic solution under high negative voltages. We explored the electro-catalytic activity of these foam deposits. For example, Figure3d shows one of the sensing electrodes on multiplexed-device after Cufoam deposition. This device is capable of oxidizing glucose in 0.1M NaOH[1a, 4] at a voltage of +0.8V(Figure3e). Therefore we assessed the linear-range between glucose concentration and device response(Figure3f). One of the parameters we have studied was reusability of multiplexed device and Figure3g shows 10-subsequest measurements studied with a single device. We have shown the application of such devices in whole serum samples and also river water for chemical oxygen demand concentration determination.
The other application we have been developing via multiplexing is immunosensor development for animal health. We have developed a simple anti-fouling matrix which allowed us to study in a complex matrix. Figure 4a summarizes the development protocol of antifouling matrix which was studied with CV after fresh antifouling coating and after incubation with either 5% BSA or serum overnight. Figure 4b shows the SEM image of one of the sensing electrode on chip after the gold deposition. We use these needle-like gold depositions as a high surface area substrate where we apply the antifouling matrix. Then, via carbodiimide chemistry we immobilized anti-Haptoglobin antibodies onto surface which is specific to haptoglobin protein (one of the immunosensors on chip). With this study we are aiming to detect several biomarkers from milk of cow after calving.

This publication has emanated from research conducted with the financial support of Science Foundation Ireland (SFI) and the Department of Agriculture, Food and Marine on behalf of the Government of Ireland under Grant Numbers [16/RC/3835), DAFM stimulus AgriSense II Grant Number 17/RD/US-ROI/56, and EU Horizon 2020 (DEMETER 857202).

[1] aV. B. Juska, A. Walcarius, M. E. Pemble, Acs Appl Nano Mater 2019, 2, 5878-5889; bV. B. Juska, M. E. Pemble, Analyst 2020, 145, 402-414.

[2] V. Buk, M. E. Pemble, Electrochimica Acta 2019, 298, 97-105.

[3] aL. A. Wasiewska, I. Seymour, B. Patella, R. Inguanta, C. M. Burgess, G. Duffy, A. O'Riordan, Sensors and Actuators B: Chemical 2021, 333, 129531; bB. O'Sullivan, B. Patella, R. Daly, I. Seymour, C. Robinson, P. Lovera, J. Rohan, R. Inguanta, A. O'Riordan, Electrochimica Acta 2021, 395.

[4] V. B. Juska, G. Juska, J Chem Technol Biot 2021, 96, 1086-1095.

Figure 1