Nanoplasmonic multiplex biosensing for COVID-19 vaccines

The ongoing emergence of severe acute respiratory syndrome caused by the new coronavirus (SARS-CoV-2) variants requires swift actions in identifying specific antigens and optimizing vaccine development to maximize the humoral response of the patient. Measuring the specificity and the amount of antibody produced by the host immune system with high throughput and accuracy is critical to develop timely diagnostics and therapeutic strategies. Motivated by finding an easy-to-use and cost-effective alternative to existing serological methodologies for multiplex analysis, we develop a proof-of-concept multiplex nanoplasmonic biosensor to capture the humoral response in serums against multiple antigens. Nanoplasmonic sensing relies on the wavelength shift of the localized surface plasmon resonance (LSPR) peak of gold nanostructures upon binding interactions between the antibodies and the immobilized antigens. Here the antigens are first immobilized on different sensing areas by using a mono-biotinylation system based on the high affinity interaction between biotin and streptavidin. We then validate the multiplex platform by detecting the presence of 3 monoclonal antibodies against 3 antigens (2 different hemagglutinins (HAs) from influenza viruses, and the SARS-CoV-2 Spike RBD (receptor binding domain)). We also measure the humoral response in murine sera collected before and after its immunization with the SARS-CoV-2 Spike protein, in good agreement with the results obtained by the ELISA assay. Our nanoplasmonic assays have successfully demonstrated multiple serum antibody profiling, which can be further integrated with microfluidics as an effective high throughput screening platform in future studies for the ongoing SARS-CoV-2 vaccine development.

Mercury vapor adsorption and sustainable recovery using novel electrothermal swing system with gold-electrodeposited activated carbon fiber cloth

A novel electrothermal swing (ETS) system with gold-electrodeposited activated carbon fiber cloth (GE-ACFC) was developed to adsorb and sustainably recover low-concentration Hg⁰. GE-ACFC with an Au growth time of 1200 s displayed the largest Hg⁰ adsorption capacity and >90% removal efficiency. The Hg⁰ adsorption of GE-ACFC was dominated by physisorption via Au amalgamation. In contrast, Hg adsorption of untreated ACFC (RAW-ACFC) was mainly controlled by physisorption and chemisorption related to carbonyl groups. Nevertheless, both ACFCs could reach 100% ETS Hg⁰ regeneration. The Hg re-adsorption of GE-ACFC was stable, with efficiency >90% at different regeneration temperatures in three-cycle ETS experiments, but the Hg re-adsorption efficiencies of RAW-ACFC greatly decreased to only 60% after 250 ℃ regeneration, due to the formation of electrothermal hot spots in the ACFC. Because the thermal and electrical conductivity of GE-ACFC increased due to Au electrodeposition, the presence of electrothermal hot spots in GE-ACFC-1200s was minor. Simulation results showed that both pseudo-first-order and pseudo-second-order models fitted well to the desorption patterns of the GE-ACFC. Mass transfer model further suggested that intraparticle diffusion control was the rate-limiting step, with diffusion coefficients increased from the first to the third cycle for GE-ACFC.

Detection of antibodies against SARS-CoV-2 spike protein by gold nanospikes in an opto-microfluidic chip

The ongoing global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to active research in its associated diagnostics and medical treatments. While quantitative reverse transcription polymerase chain reaction (qRT-PCR) is the most reliable method to detect viral genes of SARS-CoV-2, serological tests for specific antiviral antibodies are also important as they identify false negative qRT-PCR responses, track how effectively the patient's immune system is fighting the infection, and are potentially helpful for plasma transfusion therapies. In this work, based on the principle of localized surface plasmon resonance (LSPR), we develop an opto-microfluidic sensing platform with gold nanospikes, fabricated by electrodeposition, to detect the presence and amount of antibodies specific to the SARS-CoV-2 spike protein in 1μL of human plasma diluted in 1mL of buffer solution, within ∼30min. The target antibody concentration can be correlated with the LSPR wavelength peak shift of gold nanospikes caused by the local refractive index change due to the antigen-antibody binding. This label-free microfluidic platform achieves a limit of detection of ∼0.08ng/mL (∼0.5pM), falling under the clinical relevant concentration range. We demonstrate that our opto-microfluidic platform offers a promising point-of-care testing tool to complement standard serological assays and make SARS-CoV-2 quantitative diagnostics easier, cheaper, and faster.

III-V nanowire synthesis by use of electrodeposited gold particles

Semiconductor nanowires are great candidates for building novel electronic devices. Considering the cost of fabricating such devices, substrate reuse and gold consumption are the main concerns. Here we report on implementation of high throughput gold electrodeposition for selective deposition of metal seed particles in arrays defined by lithography for nanowire synthesis. By use of this method, a reduction in gold consumption by a factor of at least 300 was achieved, as compared to conventional thermal evaporation for the same pattern. Because this method also facilitates substrate reuse, a significantly reduced cost of the final device is expected. We investigate the morphology, crystallography, and optical properties of InP and GaAs nanowires grown from electrodeposited gold seed particles and compare them with the properties of nanowires grown from seed particles defined by thermal evaporation of gold. We find that nanowire synthesis, as well as the material properties of the grown nanowires are comparable and quite independent of the gold deposition technique. On the basis of these results, electrodeposition is proposed as a key technology for large-scale fabrication of nanowire-based devices.