Real-time COVID-19 detection via graphite oxide-based field-effect transistor biosensors decorated with Pt/Pd nanoparticles

Abstract

Coronavirus 2019 (COVID-19) spreads an extremely infectious disease where there is no specific treatment. COVID-19 virus had a rapid and unexpected spread rate which resulted in critical difficulties for public health and unprecedented daily life disruption. Thus, accurate, rapid, and early diagnosis of COVID-19 virus is critical to maintain public health safety. A graphite oxide-based field-effect transistor (GO-FET) was fabricated and functionalized with COVID-19 antibody for the purpose of real-time detection of COVID-19 spike protein antigen. Thermal evaporation process was used to deposit the gold electrodes on the surface of the sensor substrate. Graphite oxide channel was placed between the gold electrodes. Bimetallic nanoparticles of platinum and palladium were generated via an ultra-high vacuum (UHV) compatible system by sputtering and inert-gas condensation technique. The biosensor graphite oxide channel was immobilized with specific antibodies against the COVID-19 spike protein to achieve selectivity and specificity. This technique uses the attractive semiconductor characteristics of the graphite oxide-based materials resulting in highly specific and sensitive detection of COVID-19 spike protein. The GO-FET biosensor was decorated with bimetallic nanoparticles of platinum and palladium to investigate the improvement in the sensor sensitivity. The in-house developed biosensor limit of detection (LOD) is 1 fg/mL of COVID-19 spike antigen in phosphate-buffered saline (PBS). Moreover, magnetic labelled SARS-CoV-2 spike antibody were studied to investigate any enhancement in the sensor performance. The results indicate the successful fabrication of a promising field effect transistor biosensor for COVID-19 diagnosis.

Figure 1

Schematic representation of the fabrication steps of the GO-FET biosensor. (a) The Si/SiO₂ wafer was cleaned with acetone, ethanol, and deionized water. (b) Thermal evaporation was used to deposit the gold source and drain. (c) A graphite oxide drop was placed to form the channel. (d) Pd/Pt composite nanoparticles were sputtered on the graphite oxide channel using an Ultra High Vacuum compatible system (UHV).

Figure 2

Analysis of the spike protein by Coomassie blue staining (A) and Western blot (B). Coomassie blue staining and Western blot of the gel confirmed the presence as well the integrity of the spike protein.

Figure 3

Size distribution of composite bimetallic (Pt and Pd) nanoparticles measured using QMF.

Figure 4

SEM image of bimetallic nanoparticles of palladium and platinum.

Figure 5

EDS spectrum of composite nanoparticles. The composite nanoparticles consist of palladium and platinum with mass percentage of 4.16% for palladium, and 9.92% for platinum. The existence of other elements such as silicon (Si), and Oxygen (O) is due to the glass substrate.

Figure 6

XRD pattern of the produced Pt/Pd composite nanoparticles.

Figure 7

$I_d-V_{\mathit{ds}}$ characteristics for both GO sensors: with and without bimetallic nanoparticles.

Figure 8

(a) Schematic diagram of the GO-FET biosensor. (b) COVID-19 spike protein antibody immobilized on the GO-FET channel. (c) Target COVID-19 spike protein captured by the biosensor. (d) The electrical current variation due to capturing the spike protein. (e) Magnetic COVID-19 spike protein antibody addition. (f) The electrical current variation for the GO-FET biosensor due to Magnetic COVID-19 spike protein addition. Sensor testing.

Figure 9

Electrical characterization of GO-FET, GO-FET modified with PBASE, GO-FET with COVID-19 spike antibody-immobilized on the GO channel, and the spike protein detection.

Figure 10

Variation in the drain current due to 0.4 μL drop of 1 pg/mL of COVID-19 spike antigen for GO-FET biosensor functionalized with Middle East Respiratory Syndrome (MERS) antibody.

Figure 11

Variation in the drain current due to a 0.4 μL drop of 1 pg/mL of COVID-19 spike antigen for GO-FET biosensor functionalized with COVID-19 spike antibody (a) without nanoparticles, and (b) with Pd/Pt nanoparticles.

Figure 12

Electrical drain current for GO-FET biosensor functionalized with COVID-19 spike antibody due to 0.4 μL drop of the different concentrations of COVID-19 spike antigen.

Figure 13

Variations in the electrical drain current of FET biosensor without nanoparticles due to different concentrations of COVID-19 spike antigen without and with the addition of magnetic antibodies.

Figure 14

Variations in the electrical drain current of FET biosensor decorated with bimetallic Pd/Pt nanoparticles is due to the different concentrations of COVID-19 spike antigen without and with the addition of magnetic antibodies.