Detection of a Traumatic Brain Injury Biomarker at the 10 fg/mL Level.

BACKGROUND: The detection of minute amounts of protein biomarkers in body fluids is believed to provide early diagnosis and prognosis of mild traumatic brain injury (mTBI). An ultrasensitive detection method was used to detect S100B, the most studied potential marker for the diagnosis of mTBI. METHODS: The detection method was a modified electrochemical immunoassay technique that provides voltage controlled intrinsic current signal amplification. The sandwich immune complex of S100B was formed on the working electrode of the screen-printed electrode. The gating voltage provides amplification of the current signal that flows through the complex. RESULTS: S100B was spiked in human serum. The limit of detection of S100B in human serum was 10 fg/mL. The calibration curves cover four orders of magnitudes from 10 fg/mL to 10 ng/mL. The specificity of the detection was demonstrated using TAU protein, which is another marker for mTBI. CONCLUSION: The results reported in this work using the field effect enzymatic detection (FEED)-based immunoassay indicate the feasibility of using this method for the detection of extremely low concentrations of markers of mTBI in human serum. This method can be developed as a platform for a range of markers of mTBI.

Ultrasensitive Detection of Shigella Species in Blood and Stool.

A modified immunosensing system with voltage-controlled signal amplification was used to detect Shigella in stool and blood matrixes at the single-digit CFU level. Inactivated Shigella was spiked in these matrixes and detected directly. The detection was completed in 78 min. Detection limits of 21 CFU/mL and 18 CFU/mL were achieved in stool and blood, respectively, corresponding to 2-7 CFUs immobilized on the detecting electrode. The outcome of the detection of extremely low bacterium concentration, i.e., below 100 CFU/mL, blood samples show a random nature. An analysis of the detection probabilities indicates the correlation between the sample volume and the success of detection and suggests that sample volume is critical for ultrasensitive detection of bacteria. The calculated detection limit is qualitatively in agreement with the empirically determined detection limit. The demonstrated ultrasensitive detection of Shigella on the single-digit CFU level suggests the feasibility of the direct detection of the bacterium in the samples without performing a culture.