A label-free electrochemical impedance spectroscopy biosensor for selective detection and discrimination of the
cancer-associated sialyl-Tn (STn)
antigen was developed by using Sambucus nigra
agglutinin type I (SNA-I) as the recognition
element. The SNA-I biosensor was constructed by immobilizing the
lectin on screen-printed
gold electrodes. The formation of a complex between SNA-I and STn-containing
glycoproteins (
transferrin and
bovine submaxillary mucin) was monitored by measuring the impedance increase of the biosensor. The increase in electron transfer resistance was linearly proportional to the concentration of the
glycoproteins up to 70 ng of
transferrin and 40 ng of
bovine submaxillary mucin, with a limit of detection of 20 ng for
transferrin.
Albumin, the most abundant
serum protein, did not interfere in the detection of the STn-
glycoproteins up to a concentration of 0.2 mg ml(-1). The developed
lectin-based biosensor was used to evaluate the STn-expression in serum samples and discriminate samples from healthy individuals and patients with different types of malignant
tumors, mostly
carcinomas, where the increased expression of STn aberrant
glycans is well established. This work demonstrates the feasibility of employing SNA-I to selectively recognize the STn
epitope in
glycoproteins and the use of the constructed biosensor was effective in the analysis of serum samples with the ability to discriminate in a fast way between
cancer and healthy status. The proposed biosensor could be used for high-throughput, label-free profiling of the
cancer-associated STn
glycan expression in serum for diagnosis and
therapy monitoring.