在没有妥布霉素存在时，适体包覆在金纳米粒子（AuNPs）表面可以防止盐诱导的聚集；在妥布霉素存在时，由于适体与妥布霉素的亲和力较高，适体与妥布霉素结合并从AuNPs表面脱离，导致AuNPs在适当含量的盐中发生聚集，反应体系颜色由红色变为蓝紫色。采用基于适体修饰的金纳米粒子分光光度法测定牛奶中妥布霉素的残留量。优化的试验条件如下：适体Hp孵育时间和妥布霉素孵育时间均为15 min；反应体系的pH为7；适体Hp的浓度为1.5 μmol·L^-1；氯化钠的浓度为1.5 mol·L^-1。妥布霉素的线性范围为40.0~175 nmol·L^-1，检出限（3s/k）为13.3 nmol·L^-1。以空白样品为基体进行加标回收试验，所得回收率为96.4%~108%，测定值的相对标准偏差（n=6）为1.8%~3.0%。

In the absence of Tobramycin, the aptamer was coated on the surface of gold nanoparticles (AuNPs) to prevent salt-induced aggregation. In the presence of Tobramycin, the aptamer would separate from the surface of AuNPs and combine with Tobramycin because of the high affinity between the aptamer and Tobramycin, resulting in the aggregation of AuNPs at the appropriate content of salt, and the color of the reaction system changed from red to purple-blue. Spectrophotometry was applied to the determination of residual amount of Tobramycin in milk based on gold nanoparticles modified by aptamer. The optimized conditions found were as follows:incubation time of aptamer Hp and incubation time of Tobramycin were 15 min; pH of the reaction system was 7; concentration of aptamer Hp was 1.5 μmol·L^-1; concentration of sodium chloride was 1.5 mol·L^-1. Linearity range of Tobramycin was found between 40.0 nmol·L^-1 and 175 nmol·L^-1 with detection limit (3s/k) of 13.3 nmol·L^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 96.4%-108%, with RSDs (n=6) of determined values in the range of 1.8%-3.0%.