A novel alendronate functionalized nanoprobe for simple colorimetric detection of cancer-associated hypercalcemia

Abstract

The calcium (Ca²⁺) ion concentration in the blood serum is tightly regulated, and any abnormalities in the level of serum calcium ions are associated with many potentially dangerous diseases. Thus, monitoring of the Ca²⁺ ion concentration in the blood serum is of fundamental importance. Gold nanoparticle (GNP)-based colorimetric biosensors have enormous potential in clinical diagnostic applications due to their simplicity, versatility, and unique optical properties. In this study, we have developed an alendronate functionalized gold nanoparticle (GNP-ALD) system for the measurement of Ca²⁺ ion concentration in biological samples. The GNP-ALD system showed higher sensitivity towards the Ca²⁺ ion compared to adenosine diphosphate (ADP) or adenosine triphosphate (ATP). The strong interaction between the Ca²⁺ ion and ALD at the GNP/solution interface resulted in significant aggregation of the ALD conjugated GNPs, and induced a color change of the solution from red to blue, which could be visually observed with the naked eye. The interaction between the Ca²⁺ ion and GNP-ALD was characterized by UV-visible spectroscopy, transmission electron microscopy (TEM) imaging, and dynamic light scattering (DLS) analysis. Under the optimized conditions, the lower limit of Ca²⁺ ion detection using this method was found to be 25 μM and a linear response range from 25 μM to 300 μM Ca²⁺ ions was obtained with excellent discrimination against other metal ions. The GNP-ALD nanoprobe could successfully determine the ionized Ca²⁺ concentration in various serum samples and the results were validated using a commercial calcium assay kit. Moreover, as a practical application, we demonstrated the utility of this nanoprobe for the detection of cancer-associated hypercalcemia in a mouse model.