A bio probe was firstly prepared by assembling sulfhydryl DNA on the surface of Au nanoparticles(AuNPs).Then the 3′-OH end on the probe DNA was extended under the catalysis of terminal deoxynucleotidyl transferase(TdTase)

and produced a long single chain DNA(single stranded DNA

ssDNA).The probe and the long ssDNA were characterized by agarose gel electrophoresis and atomic force microscopy(AFM).Results showed that

under the action of TdTase

DNA containing 3′-OH achieved an efficient extension at the nano interface

and the chain length was up to 850 nm though it was in the irregular coiled state.Afterwards

this DNA growth strategy combined with aptamer technology was applied to construct an aptasensor for the detection of enrofloxacin(ENR).The aptamer fragment 1 was firstly assembled on the surface of the AuNPs

then the aptamer fragment 2 was assembled on the surface of the magnetic particle activated by glutaraldehyde.After experiencing the TdT-mediated DNA growth strategy

the aptasensor had a good response to ENR concentration in the range of 10-10×105 ng/mL with a detection limit of 10 ng/mL.At the same time

the detection signal for enrofloxacin was significantly different from those for ciprofloxacin

ofloxacin

norfloxacin and other control groups.The results showed that the TdTase based aptasensor could provide a new research idea or method for food safety detection and other fields with the advantages of convenient operation

good sensitivity and excellent specificity.