Fig. 5: Detection of SARS-CoV-2 antibodies in human saliva.

a, Distribution of IgG MFI signals from the saliva of COVID-19-positive patients (‘P’, n = 10) compared to healthy controls (‘H’, n = 23) against both S1 and RBD, with the inset showing a noticeable difference between the weak IgG signals from COVID-19 saliva and signal noise from that of healthy saliva. b, A confocal fluorescence image of IgG signals in the saliva of patients who had recovered from COVID-19 (n = 4, denoted P1–P4, in red) and healthy controls (n = 11, denoted P5–P15) and 10⁴ times diluted serum of a patient with PCR-confirmed COVID-19 as a reference (denoted Ref, in red). The human IgG control spots are located on rows 1 and 7, intrawell signal normalizer spots are on row 2, RBD spots are on row 4, and S1 spots are on row 6 in each microarray. c, MFI signals of anti-S1 and anti-RBD IgG measured in saliva samples (P1–P15) and a PCR-positive COVID-19 serum reference (Ref) from the biochip seen in b, with background signals subtracted. The MFI of healthy controls was near background noise, as shown in the inset. Error bars indicate one standard deviation from the mean of the MFI signals detected against the respective microarrayed antigen spots (n = 3). The raw data corresponding to b and c are provided in Supplementary Table 9.