When negative controls, i.e. unconjugated QDs (UN-QDs) or QD conjugated to irrelevant sdAbs (gp120-QDs) were applied onto thin agarose sections of high-HER2-expressing tumours, no comparable signals at the tumour cell membrane were detected (Fig. 2A, third and fourth column), which reflected the high specificity and sensitivity of sdAb-HER2-QDs for binding to HER2-expressing tumour cells. Here, ITIH4 is linked to neoplasm.