Preliminary Development of DNA Aptamer Quantum Dot-Based Competitive Lateral Flow Assays for Saxitoxin and Tetrodotoxin

Initial proof-of-concept development of competitive lateral flow (LF) test strips involving red quantum dots (Qdots) is demonstrated with visible confirmation of the competitive displacement of Qdot-protein-saxitoxin (Stx) and -tetrodotoxin (Ttx) conjugates over 15 min. The measured limits of detection (LODs) for the best versions of the assays were in the 1-2 µg range when a bovine serum albumin (BSA)-Stx or -Ttx conjugate was used as the analyte for safety reasons and NIH ImageJ image analysis was applied. However, when one assumes that only one of the primary amines in BSA labeled with Stx or Ttx is needed as the "epitope" for capture and calculates the weight of the toxin adducts on an equal mole basis to that of 1 µg of toxin-BSA conjugate, the LODs are as low as 4.5 ng of toxin. No cross-reactivity was seen for these prototype test strips when BSA-Stx and BSA-Ttx were switched as analytes at or near their respective LODs which is in agreement with published specificity and affinity studies for these aptamers in the literature.