Molecular Beacon-Based Fluorescent Assay for Specific Detection of Oversulfated Chondroitin Sulfate Contaminants in Heparin without Enzyme Treatment

Oversulfated chondroitin sulfate (OSCS) is a harmful coutaminant in the pharmaceutical heparin. The development of a rapid,, convenient, Sensitive, and Selective method is required for routine analysis of OSCS in pharmaceutical heparin. Here we report a simple, rapid; sensitive, and enzyme-free method for detecting OSCS in heparin based on the competitive binding between OSCS and the adenosine-repeated molecular beacon (MB) stem to coralyne in the presence of Ca2+ ions. The MB (A(8)-MB-A(8)) contains a 22-mer loop, a stem of a pair of 8-mer adenosine (A) bases, a fluorophore unit at the S'-end, and a quencher at the 3'-end. The presence of coralyne promotes these A A. mismatches to form a hairpin-shaped MB. However, this kind of MB is incapable of differentiating between heparin and OSCS because they both exhibit strong electrostatic attraction with coralyne. This study found that while Ca2+ ions can efficiently suppress the negative charges of heparin, they do not neutralize the negative charge of OSCS. Thus, in the presence of Ca2+ ions, OSCS can remove coralyne from the MB stein, initiating fluorescence of the MB. Under optimal conditions (10 nM A(8)-MB-A(8), 800 nMicoralyne, and 0.5 mM Ca2+ ions), the proposed system can detect 0.01% w/w OSCS in heparin in under 5 mkt Without enzyme treatment. This study also validates the practicality of the proposed system to determine 0:01% w/w OSCS in the pharmaceutical heparin.