Developing Topics.

Background: A novel improvement to Quanterix Corporation Single molecule array (Simoa) SR-X instrument has been shown to offer up to 100-fold increased sensitivity compared with standard Simoa HD-X and SR-X instruments. We independently validated this increased sensitivity using the Simoa interleukin 17A (IL17A) assay.

Method: IL17A was measured in 32 paired Alzheimer's disease (AD; n = 13) and control (CTRL; n = 19) serum and cerebrospinal fluid (CSF) samples. Mean IL17A concentrations were compared in both biofluids measured using four Simoa instruments - one HD-X instrument and three SR-X instruments modified to improve the efficiency of reading beads.

Result: HD-X quantified IL17A in 0% of CSF samples and 37.5% of serum samples, with mean serum IL17A concentrations of 0.126pg/mL in AD and 0.228pg/mL in CTRLs. In contrast, the modified SR-X instruments A, B and C quantified CSF IL17A in 84.4%, 96.9% and 96.9% of CSF samples, respectively, with mean AD concentrations of 2.92fg/mL, 5.95fg/mL and 7.25fg/mL, respectively, and mean CTRL concentrations of 3.60fg/mL, 4.75fg/mL and 9.02fg/mL, respectively. Furthermore, the modified SR-X instruments A, B and C all quantified IL17A in 100% of serum samples, with mean serum AD concentrations of 0.145pg/mL, 0.285pg/mL, and 0.249pg/mL, respectively, and mean CTRL concentrations of 0.300pg/mL, 0.406pg/mL and 0.362pg/mL, respectively. There were no statistically significant intra-instrument differences between AD compared with CTRLs. All three modified SR-X serum concentrations showed a strong positive statistically significant correlation with HD-X serum concentrations. All three modified SR-X serum concentrations also showed a strong positive statistically significant correlation with one another. Finally, all three modified SR-X instruments showed no correlation between serum and CSF concentrations, in line with previous literature.

Conclusion: Increasing the bead reading efficiency of the SR-X exhibits increased sensitivity compared with the standard Simoa HD-X instrument, allowing the quantification of IL17A in CSF and a greater yield of serum samples.