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Nanotherapeutics has an increasing role in the treatment of diseases such as cancer. In photodynamic therapy (PDT) a therapeutically inactive photosensitizer compound is selectively activated by light to produce molecules capable of killing diseased cells and pathogens. A phototheranostic agent can be defined as a single nanoentity with the capabilities for targeted delivery, optical imaging and photodynamic treatment of a disease. Malignant cells, tissue and microbial etiologic agents can be effectively targeted by PDT. Photodynamic therapy is noninvasive, or minimally invasive, and has few side effects as damage to healthy tissue is minimized and the killing effect is localized. Various forms of cancer, acne and other diseases may be treated. The in vivo efficacy of photosensitizers is further improved by attaching them to nanostructures capable of targeting the diseased site. Such photosensitizer-functionalized nanostructures, or nanotherapeutics, allow site-specific delivery of imaging and therapeutic agents for improved phototheranostic performance. This review explores the potential applications of phototheranostic nanostructures in diagnosis and therapy.

Bioinspired synthesis of nanomaterials is highly advantageous as a natural and cost-effective resource. Development of noble metal nanotheranostic agents was achieved through bioinspired synthetic routes. These biosynthesized nanoparticles were characterized by various analytical techniques including absorption spectroscopy, FTIR and electron microscopy (SEM and TEM). A large number of medicinal plants were screened, among which Potentilla f ulgens (PF, vajradanti) and Camellia sinensis (CS, green tea) were found to produce nanomaterials with higher yields. Plant (PF and CS) mediated metallic nanoparticles had added advantage of metal reduction and simultaneous phytochemical capping over chemically synthesized procedures, which require multiple reagents. Antioxidant potential of the nanomaterials was determined by in vitro antioxidant assays confirming substantial antioxidant properties, which was due to the presence of phytochemicals on the nanoparticle surface. Flavonoids and catechins on the nanomaterial surface served as the supplier of hydroxyl groups for further derivatization. The surface of the nanoparticles was engineered by conjugating imaging and therapeutic moieties, resulting in the formation of theranostic nanoagents. The multimodal agents were characterized and the extent of drug loading was determined to validate the efficacy of those nanoconjugates. These bioinspired multimodal nanoprobes can serve as essential diagnostic and therapeutic tools in ongoing biomedical research.

A simple and efficient eco-friendly approach for the biosynthesis of stable, monodisperse silver nanoparticles (AgNPs) using Rhododendron dauricum flower extract is described. Different reaction parameters (concentration of plant extract, substrate concentration, pH, temperature and reaction time)were optimized to synthesize AgNPs with controlled properties. AgNPs were characterized in terms of synthesis, size distribution (PDI of 0.25), capping functionalities (phenolic compounds) and microscopic evaluation by UV-Visible spectroscopy, dynamic light scattering, Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscope (TEM). The specific characteristics and loss of organic content (1.81 mg) of the synthesized nanoparticles was measured by Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA). The results showed the simplistic and feasible approach for obtaining stable aqueous monodispersive AgNPs. Further, the antioxidant activity of AgNPs imparted by plant phenolic components was evaluated using DPPH assay and found to be comparable to standard TROLOX.

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