[International multi-center evaluation of a rapid antigen test based on gold immunochromatographic assay for detection of severe acute respiratory syndrome coronavirus 2]

Objective: The gold immunochromatographic assay for detection of SARS-CoV-2 antigen was evaluated by international multi-center clinical trial. Methods: A total of 1 855 clinical parallel samples with valid test results (for nucleic acid and antigen tests, respectively) were collected from nine countries, including Germany, the United Kingdom, Ukraine, France, India, Thailand, Malaysia, the United States of America and Brazil, with sampling period from January 3 to September 22, 2021. These samples were detected by SARS-CoV-2 antigen test kit (colloidal gold immunochromatography assay) and nucleic acid detection kit (real-time fluorescent quantitative reverse transcription polymerase chain reaction). Positive coincidence rates [(number of antigen-positive cases/nucleic acid-positive cases)×100%], negative coincidence rates [(number of antigen-negative cases/nucleic acid-negative cases)×100%], total coincidence rates [(number of cases with consistent results for both antigen and nucleic acid detection/number of total cases) ×100%], as well as Kappa values were calculated. The differences of the above indictors among different countries were evaluated by the coefficient of variation. The detection rates of the antigen test for samples with different cycle threshold values (Ct values) for the nucleic acid detection, different characteristics and different mutant strains were analyzed. Results: For all samples, the positive, negative, and total coincidence rate between the antigen test and nucleic acid assay was 90.8% (569/627), 99.7% (1 224/1 228) and 96.7% (1 793/1 855), respectively, and the consistency coefficient Kappa value was 0.924. Among these countries, the coefficient of variation for positive coincidence rates (except for Malaysia with a lot of samples with Ct value>30), negative coincidence rates (except for France without negative samples) and total coincidence rates (except for France) was 6%,<1%, and 6%, respectively. When Ct values were less than 25, the detection rates of antigen test were 83.3%-100% for each countries (the coefficient of variation was 6%); the total detection rate and the coefficient of variation was 93.4% (428/458) and 5%, respectively, for asymptomatic infected persons and cases within 7 days post onset of symptoms; the total detection rate for various SARS-CoV-2 mutant strains was 97.5% (119/122); and it showed negative results for samples from cases infected with other viruses, including influenza A virus subtype H1N1, influenza B virus, respiratory syncytial virus subgroups A and B, coxsackievirus 16, human metapneumovirus, parainfluenza virus types 1 and 4, Epstein-Barr virus and adenovirus. Conclusion: The SARS-CoV-2 antigen test kit showed excellent authenticity, and there were few differences for its indictors among nine countries, therefore it can meet the needs of large-scale early screening of SARS-CoV-2 infection.

[International multi-center evaluation of a rapid antigen test based on gold immunochromatographic assay for detection of severe acute respiratory syndrome coronavirus 2]

Objective: The gold immunochromatographic assay for detection of SARS-CoV-2 antigen was evaluated by international multi-center clinical trial. Methods: A total of 1 855 clinical parallel samples with valid test results (for nucleic acid and antigen tests, respectively) were collected from nine countries, including Germany, the United Kingdom, Ukraine, France, India, Thailand, Malaysia, the United States of America and Brazil, with sampling period from January 3, 2021 to September 22, 2021. These samples were detected by SARS-CoV-2 antigen test kit (colloidal gold immunochromatography assay) and nucleic acid detection kit (real-time fluorescent quantitative reverse transcription polymerase chain reaction). Positive coincidence rates [(number of antigen-positive cases/nucleic acid-positive cases)×100%], negative coincidence rates [(number of antigen-negative cases/nucleic acid-negative cases)×100%], total coincidence rates [(number of cases with consistent results for both antigen and nucleic acid detection/number of total cases) ×100%], as well as Kappa values were calculated. The differences of the above indictors among different countries were evaluated by the coefficient of variation. The detection rates of the antigen test for samples with different cycle threshold values (Ct values) for the nucleic acid detection, different characteristics and different mutant strains were analyzed. Results: For all samples, the positive, negative, and total coincidence rate between the antigen test and nucleic acid assay was 90.8% (569/627), 99.7% (1 224/1 228) and 96.7% (1 793/1 855), respectively, and the consistency coefficient Kappa value was 0.924. Among these countries, the coefficient of variation for positive coincidence rates (except for Malaysia with a lot of samples with Ct value>30), negative coincidence rates (except for France without negative samples) and total coincidence rates (except for France) was 6%,<1%, and 6%, respectively. When Ct values were less than 25, the detection rates of antigen test were 83.3%-100% for each countries (the coefficient of variation was 6%); The total detection rate and the coefficient of variation was 93.4% (428/458) and 5%, respectively, for asymptomatic infected persons and cases within 7 days post onset of symptoms; the total detection rate for various SARS-CoV-2 mutant strains was 97.5% (119/122); and it showed negative results for samples from cases infected with other viruses, including influenza A virus subtype H1N1, influenza B virus, respiratory syncytial virus subgroups A and B, coxsackievirus 16, human metapneumovirus, parainfluenza virus types 1 and 4, Epstein-Barr virus and adenovirus. Conclusion: The SARS-CoV-2 antigen test kit showed excellent authenticity, and there were few differences for its indictors among nine countries, therefore it can meet the needs of large-scale early screening of SARS-CoV-2 infection.

Origin of third-order optical nonlinearity in Au:SiO(2) composite films on femtosecond and picosecond time scales

Three sorts of probe laser, which have pulse durations of 200 fs, 35 ps, and 70 ps, were employed in the measurement of the third-order nonlinear optical susceptibility x((3)) in Au:SiO(2) composite films in a degenerate four-wave mixing scheme. We found that the composite films at their absorption peak (~550 nm) had a maximum x((3)) , which depends strongly on the pulse width of the probe laser. The value of x((3)) measured with a 70-ps laser was ~30 times larger than that measured with a 200-fs laser. The time-resolved measurements revealed that the optical nonlinearity on the femtosecond time scale is attributable mainly to contributions from the interband electric-dipole transition (especially at low concentrations) and partly to those from hot electrons rather than being dominated by hot-electron excitation in the picosecond regime.

Second-harmonic generation in quasi-periodically domain-inverted Sr(0.6) Ba(0.4) Nb(2)O(6) optical superlattices

One-dimensional Fibonacci-type quasi-periodically domain-inverted structures have been successfully fabricated in a strontium barium niobate crystal by electric field poling. With a single such structure, type I phase-matched second-harmonic generation (SHG) has been demonstrated at several wavelengths from red to near ultraviolet. The spectral positions of the observed SHG peaks are in good agreement with theoretical predictions. The range of measured conversion efficiencies is 2-10%.