Figure 1 schematically illustrates the function of the designed mixed-sized GNP LFA for BSA detection. Because serum albumin (SA) is a major circulatory protein present in the intravascular and interstitial spaces between cells, it was selected as the ideal target model to analytically evaluate the detection performance of our proposed strategy. Furthermore, SA can be used as a biomarker for the early detection of chronic kidney disease because it has been reported that a concentration of albumin in urea at ≥3.0 g dL−1 is closely associated with chronic kidney disease [13,14]. The gene discussed is ALB; the disease is chronic kidney disease.