New, stable, and glyoco-derivatized gold nanorods (GNRs) were prepared using developed amphiphilic block glycopolymers poly[(lactose)(m)-b-(pyridine)(n)] to engineer self-organized, densely packed glycopolymeric recognition layers and generate a multivalent binding cavity onto the gold surface. We report a rapid and ultrasensitive biosensing for the weak affinity of protein-carbohydrate binding employing a combination of the longitudinal SPR of GNRs and the cluster glycoside effect. Thus, a very small amount of lectin (100 pg mL(-1) = 8.3 x 10(-13) M) was detected by the aggregation of GNRs.