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A UV-visible spectroscopic detection method of kanamycin was successfully developed based on target-induced growth of gold nanoparticles (AuNPs), using AuNPs as the probe and a kanamycin-specific aptamer as the recognition element. Firstly, the aptamer was incubated with AuNPs, which blocked the surface of the AuNPs, and inhibited the further growth of AuNPs. However, kanamycin bound with the aptamer on the surface of AuNPs with high affinity, competitively desorbed the aptamer and exposed the surface of AuNPs. Then, the growth of AuNPs proceeded by addition of NH2OH and HAuCl4. After the growth of AuNPs, the color and the maximum absorption wavelength of the AuNP solution changed, which was utilized to determine the concentration of kanamycin. Under the optimized conditions, the proposed UV-visible spectroscopic assay showed high sensitivity and high specificity for kanamycin, with a linear detection range from 20 to 100 nM, and the detection limit of 9.21 nM. Moreover, the assay has been successfully applied to detect kanamycin in honey samples without pretreatment. Therefore, it has great application prospects to detect residual kanamycin in food, medicine and water environments.

A sensitive simultaneous detection of streptomycin (STR), chloramphenicol (CHL) and tetracycline (TET) residues was achieved based on aptamers and quantum dot (QD) tags. Three complementary DNA1 sequences (cDNA1s) were first designed, which are not only complementary to corresponding aptamer DNAs (Ap-DNAs) specific for STR, CHL and TET, but also complementary to part of capture DNAs (Cap-DNAs) and part of complementary DNA2s (cDNA2s), respectively. cDNA1s initially hybridize with corresponding Ap-DNAs to form duplex DNAs. However, when the target antibiotics are present, STR, CHL and TET can bind with their Ap-DNAs specifically with higher affinity, which leads to the release of cDNA1s. Then the liberated cDNA1s hybridize with corresponding Cap-DNAs which are immobilized on the surface of a gold electrode by self-assembly. After that, the prepared PbS, CdS and ZnS QDs-tagged cDNA2s further hybridize with the other ends of corresponding cDNA1s on the electrode surface. The captured QDs yield distinct electrochemical signals after acid dissolution, which reflect the type and concentration of target antibiotics. Due to the inherent amplification feature of QD tags, the low detection limits for STR, CHL and TET reached 10 nM, 5 nM and 20 nM, respectively. In addition, the established assay was applied in the detection of STR, CHL and TET residues in milk samples and showed similar response ranges.

A highly sensitive spectrophotometric method for ethyl carbamate (EC) determination was established through glutamate dehydrogenase/urethanase cascade reactions and the corresponding change in NADH concentration. The absorbance at 340 nm is linearly related to the EC concentration within the range of 0.3–50 μM, with a low detection limit of 0.00928 μM. The assay was further applied to analyse EC in mimic Chinese rice wine samples.

Aminoglycoside antibiotics are widely used drugs. The residual antibiotics in animal-derived food are proven to be harmful to human health and therefore should be strictly controlled in the food industry. A spectrophotometric method based on a kanamycin-specific aptamer and gold nanoparticles (AuNPs) was developed for the quantitative detection of kanamycin. Two types of functionalized AuNPs were synthesized by self-assembly of thiol-modified single-stranded DNAs (ssDNAs), which were complementary to the 5′ terminal and 3′ terminal sequences of the kanamycin aptamer. As the kanamycin aptamer is mixed with these AuNPs, the AuNPs aggregate due to the hybridization of the aptamer with the complementary ssDNAs on the surface of AuNPs. However, when different concentrations of kanamycin are present, it can bind with the aptamer specifically and competitively, which leads to the disaggregation of the AuNPs aggregate, and a change in the UV-visible absorption spectrum of AuNPs. The absorbance at 527 nm is utilized to detect the concentration of kanamycin. The detection range of this method is 1–500 nM, with a detection limit of 1 nM. The developed method was then successfully employed to detect kanamycin in milk samples, and a similar response range and detection limit were obtained.