Probing multifunctional azure B conjugated gold nanoparticles with serum protein binding properties for trimodal photothermal, photodynamic, and chemo therapy: Biophysical and photophysical investigations.

Multimodal or combination therapy has been considered as a powerful approach for treatment of complex diseases like cancer. The fascinating physicochemical and optoelectronic properties of gold nanoparticles make them potential candidate for cancer therapeutic and diagnostic applications. Herein, we design a multifunctional nanosystem by conjugating a photosensitizer, Azure B (AB) with citrate reduced gold nanoparticles (CI-Au NPs) through non-covalent interactions. The conjugation of AB with CI-Au NPs was confirmed through UV-Visible absorption spectroscopy and Fourier Transform Infra-red (FT-IR) spectroscopy. The morphology, size, and charge of the prepared nano-conjugates (AB@CI-Au NPs) were determined by transmission electron microscopy (TEM), Dynamic light scattering (DLS), and zeta potential measurements. The proficiency of AB@CI-Au NPs for cancer photo-therapies was demonstrated by evaluating their potential for photothermal heating and singlet oxygen generation in solution upon Visible laser (635 nm, 500 mW/cm2) irradiation. The AB@CI-Au NPs display superior heating efficiency than CI-Au NPs alone or free AB, and offer better photostability as well as singlet oxygen generation rate compared to free photosensitizer. The interaction of AB@CI-Au NPs with Calf thymus DNA (Ct-DNA) and transport protein Bovine Serum Albumin (BSA) were studied using various biophysical techniques including Circular dichroism, UV-Visible and fluorescence spectroscopic studies. AB@CI-Au NPs show intercalative binding with Ct-DNA by inducing local perturbations in double helical structure and hence can exert chemotherapeutic action by targeting DNA. AB@CI-Au NPs also display moderate binding with BSA without any adverse effect on BSA structure, which is desirable for significant biodistribution and pharmacokinetics of AB@CI-Au NPs. Also, in vitro cytotoxicity of the AB@CI-Au NPs with and without laser irradiation (635 nm, 500 mW/cm2) was demonstrated using the hepatocellular carcinoma (HepG2) cell lines. Our findings through photophysical and biophysical studies strongly recommend the exploitation of AB@CI-Au NPs nanoconjugates as a multifunctional probe for trimodal anticancer therapy.