Boron doped diamond thin films for the electrochemical detection of SARS-CoV-2 S1 protein.

Amidst a global pandemic, a precise and widely accessible rapid detection method is needed for accurate diagnosis and contact tracing. The lack of this technology was exposed through the outbreak of SARS-CoV-2 beginning in 2019. This study sets the foundation for the development of a boron doped diamond (BDD)-based impedimetric sensor. While specifically developed for use in the detection of SARS-CoV-2, this technology uses principles that could be adapted to detect other viruses in the future. Boron doped polycrystalline diamond electrodes were functionalized with a biotin-streptavidin linker complex and biotinylated anti-SARS-CoV-2 S1 antibodies. Electrodes were then incubated with the S1 subunit of the SARS-CoV-2 spike surface protein, and an electrical response was recorded using the changes to the electrode's charge transfer resistance (Rct), measured through electrochemical impedance spectroscopy (EIS). Detectable changes in the Rct were observed after 5-min incubation periods with S1 subunit concentrations as low as 1 fg/mL. Incubation with Influenza-B Hemagglutinin protein resulted in minimal change to the Rct, indicating specificity of the BDD electrode for the S1 subunit of SARS-CoV-2. Detection of the S1 subunit in a complex (cell culture) medium was also demonstrated by modifying the EIS protocol to minimize the effects of sample matrix binding. BDD films of varying surface morphologies were investigated, and material characterization was used to give insight into the microstructure-performance relationship of the BDD sensing surface.

Stable Ultra-thin Silver Films Grown by Soft Ion Beam-Enhanced Sputtering with an Aluminum Cap Layer.

Ultra-thin silver films are susceptible to ambient environments and form grayish layers in the silver mirroring process. The poor wettability together with the high diffusivity of surface atoms in the presence of oxygen accounts for the thermal instability of ultra-thin silver films in the air and at elevated temperatures. This work demonstrates an atomic-scale aluminum cap layer on the silver to enhance the thermal and environmental stabilities of ultra-thin silver films deposited by sputtering with the assistance of a soft ion beam reported in our previous work. The resulted film consists of an ion-beam-treated seed silver layer of ∼1 nm nominal thickness, a subsequent silver layer of ∼6 nm thickness produced by sputtering alone, and an aluminum cap layer of ∼0.2 nm nominal thickness. Although the aluminum cap is only one to two atomic layers and likely non-continuous, it significantly improved the thermal and ambient environmental stability of the ultra-thin silver films (∼7 nm thick) without affecting the film's optical and electrical properties. The improved environmental stability is attributed to the cathodic protection mechanism and reduced diffusivity of surface atoms. The improved thermal stability is attributed to the reduced mobility of surface atoms in the presence of aluminum atoms. Thermal treatment of the duplex film also improves the film's electrical conductivity and optical transmittance by enhancing its crystallinity. The annealed aluminum/silver duplex structure has exhibited the lowest electric resistivity among the reported ultra-thin silver films and high optical transmittance similar to the simulated theoretical results.

Single-beam plasma source deposition of carbon thin films.

A single-beam plasma source was developed and used to deposit hydrogenated amorphous carbon (a-C:H) thin films at room temperature. The plasma source was excited by a combined radio frequency and direct current power, which resulted in tunable ion energy over a wide range. The plasma source could effectively dissociate the source hydrocarbon gas and simultaneously emit an ion beam to interact with the deposited film. Using this plasma source and a mixture of argon and C2H2 gas, a-C:H films were deposited at a rate of ∼26 nm/min. The resulting a-C:H film of 1.2 µm thick was still highly transparent with a transmittance of over 90% in the infrared range and an optical bandgap of 2.04 eV. Young's modulus of the a-C:H film was ∼80 GPa. The combination of the low-temperature high-rate deposition of transparent a-C:H films with moderately high Young's modulus makes the single-beam plasma source attractive for many coatings applications, especially in which heat-sensitive and soft materials are involved. The single-beam plasma source can be configured into a linear structure, which could be used for large-area coatings.