Spectral image contrast-based flow digital nanoplasmon-metry for ultrasensitive antibody detection.

BACKGROUND: Gold nanoparticles (AuNPs) have been widely used in local surface plasmon resonance (LSPR) immunoassays for biomolecule sensing, which is primarily based on two conventional methods: absorption spectra analysis and colorimetry. The low figure of merit (FoM) of the LSPR and high-concentration AuNP requirement restrict their limit of detection (LOD), which is approximately ng to µg mL-1 in antibody detection if there is no other signal or analyte amplification. Improvements in sensitivity have been slow in recent for a long time, and pushing the boundary of the current LOD is a great challenge of current LSPR immunoassays in biosensing. RESULTS: In this work, we developed spectral image contrast-based flow digital nanoplasmon-metry (Flow DiNM) to push the LOD boundary. Comparing the scattering image brightness of AuNPs in two neighboring wavelength bands near the LSPR peak, the peak shift signal is strongly amplified and quickly detected. Introducing digital analysis, the Flow DiNM provides an ultrahigh signal-to-noise ratio and has a lower sample volume requirement. Compared to the conventional analog LSPR immunoassay, Flow DiNM for anti-BSA detection in pure samples has an LOD as low as 1 pg mL-1 within only a 15-min detection time and 500 µL sample volume. Antibody assays against spike proteins of SARS-CoV-2 in artificial saliva that contained various proteins were also conducted to validate the detection of Flow DiNM in complicated samples. Flow DiNM shows significant discrimination in detection with an LOD of 10 pg mL-1 and a broad dynamic detection range of five orders of magnitude. CONCLUSION: Together with the quick readout time and simple operation, this work clearly demonstrated the high sensitivity and selectivity of the developed Flow DiNM in rapid antibody detection. Spectral image contrast and digital analysis further provide a new generation of LSPR immunoassay with AuNPs.

A nanofluidic preconcentrator integrated with an aluminum-based nanoplasmonic sensor for Epstein-Barr virus detection

Epstein-Barr virus (EBV) positivity is one of the indexes for diagnosing nasopharyngeal carcinoma (NPC). Moreover, systemic inflammatory responses can easily be triggered in patients who are both EBV- and coronavirus disease 2019 (COVID-19)-positive. Development of rapid and highly sensitive EBV screening methods has become important. In this study, a nanofluidic preconcentrator integrated with a nanoslit Fano resonance biosensor was developed to detect latent membrane protein 1 (LMP1) for an EBV diagnosis. Through nanoimprinting and aluminum deposition, the low-cost nanoslit plasmonic sensing chip can be mass-produced. The nanoporous membrane was patterned on a sensing chip as an ion selective channel to concentrate LMP1 proteins. Anti-LMP1 immunoglobulin G was then modified to a sensing chip to immunosense LMP1. The Fano resonant spectrum of the capped nanoslit array produced a transmission peak followed by a dip. We recorded and analyzed the spectrum using four methods, including area, center of mass, peak value, and dip value methods. With preconcentration, a limit of detection (LOD) of 100pg/ml and a sensing range of 100pg/ml to 10µg/ml was achieved using the peak value.

Dispersion-enhancing surface treatment of AuNPs for a reduced probe loading and detection limit using t-SPR detection.

COVID-19 has shown that a highly specific and rapid diagnostic system is a necessity. A spectral imaging-based surface plasmon resonance (SPRi) platform with an integrated microfluidic biosensor to detect oligonucleotide sequences has been proposed to be a promising alternative for infectious diseases due to its safe and straightforward use. Approaches to reduce the DNA probe loading onto gold nanoparticles with various types of polyethylene glycol (PEG) were explored. Here, we demonstrated the stability of functionalised gold nanoparticles with unmodified PEG whilst lowering the probe loading density. The system was evaluated by performing the detection of a mimicking COVID-19 target sequence, single point-mutation sequence and fully mismatch sequence. Highly specific binding of the mimicking COVID-19 target sequence was observed and analysed by the spectral imaging SPR approach. Our work has demonstrated the potential of a controlled probe density using unmodified PEG as an especially promising functionalisation strategy in SPR spectral imaging assays.