Abstract
The toxicity of heavy metals present in binary semiconductor nanoparticles also known as quantum dots (QDs) has hindered their wide applications hence the advent of non-toxic ternary quantum dots. These new group of quantum dots have been shown to possess some therapeutic action against cancer cell lines but not significant enough to be referred to as an ideal therapeutic agent. In this report, we address this problem by conjugating red emitting CuInS/ZnS QDs to a 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin -photosensitizer for improved bioactivities. The glutathione capped CuInS/ZnS QDs were synthesized in an aqueous medium using a kitchen pressure cooker at different Cu: In ratios (1:4 and 1:8) and at varied temperatures (95 °C, 190 °C and 235 °C). Optical properties show that the as-synthesized CuInS/ZnS QDs become red-shifted compared to the core (CuInS) after passivation with emission in the red region while the cytotoxicity study revealed excellent cell viability against normal kidney fibroblasts (BHK21). The highly fluorescent, water-soluble QDs were conjugated to 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) via esterification reactions at room temperature. The resultant water-soluble conjugate was then used for the cytotoxicity, fluorescent imaging and gene expression study against human monocytic leukemia cells (THP-1). Our result showed that the conjugate possessed high cytotoxicity against THP-1 cells with enhanced localized cell uptake compared to the bare QDs. In addition, the gene expression study revealed that the conjugate induced inflammation compared to the QDs as NFKB gene was over-expressed upon cell inflammation while the singlet oxygen (1O2) study showed the conjugate possessed large amount of 1O2, three times than the bare porphyrin. Thus, the as-synthesized conjugate looks promising as a therapeutic agent for cancer therapy.
Highlights
The use of nanomaterials for biological application has in the past decade transpired as a promising avenue to explore for biological application due to their size, shape, specific surface area, aspect ratio and surface chemistry
Glutathione-capped CuInS based quantum dots (QDs) were synthesised at large scale using a non-injection hydrothermal method in a household pressure cooker
The CuInS QDs red-shifted from 525 nm to 607 nm and 503 nm to 613 nm at ratio 1:4 and 1:8 respectively. This red shifting after the shell formation reported for the first time for aqueous synthesised ternary CuInS based QDs is attributed to the dominance of quantum confinement effect over cation exchange process
Summary
The use of nanomaterials for biological application has in the past decade transpired as a promising avenue to explore for biological application due to their size, shape, specific surface area, aspect ratio and surface chemistry. Despite the vast amount of work reported on the application of binary QDs by various groups[8,9], the clinical use of the binary QDs has been limited by the presence of toxic heavy metals (Cd, Pb, Hg) in their composition This has prompted the investigation of less-toxic alternative materials composed of group I (Cu, Ag), group III (In, Ga, Al) and group VI (S, Se, Te) elements called “ternary” quantum dots. To the best of our knowledge, this red shifting after the shell formation has never been reported for aqueous synthesized ternary CuInS based QDs. Cell viability studies of the CuInS/ZnS QDs on normal kidney fibroblast cell line (BHK21) showed the material possess excellent viability towards healthy cells. Based on the good results obtained from the in vitro study against the leukaemia cell line, the singlet oxygen generation (SOQY) ability of the conjugate was evaluated
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