Eugenia Li Ling Yeo

Exploiting the protein corona around gold nanorods for low-dose combined photothermal and photodynamic therapy

A nanodevice comprising human serum (HS) protein corona coated gold nanorods (NRs) has been developed to perform both photothermal therapy (PTT) and photodynamic therapy (PDT) simultaneously at a very low dose under irradiation by a single laser. Here, we exploit the protein corona to load a photosensitizer, chlorin e6 (Ce6), to form NR-HS-Ce6, whose excitation wavelength matches with the longitudinal surface plasmon resonance (LSPR) of NRs. When excited by a single laser, the NRs caused photothermal ablation of cancer cells while Ce6 simultaneously produced reactive oxygen species (ROS) to kill cancer cells through oxidative stress in PDT. We found that the protein corona did not affect the photothermal heating of NRs and observed more than 5-fold increase in ROS generation when Ce6 was loaded on NR-HS compared to free HS-Ce6 dissolved in HS. The uptake of Ce6 by Cal 27 oral squamous cell carcinoma (OSCC) cells also increased 57-fold when loaded on NR-HS compared to free HS-Ce6. While both PDT and PTT have established modest success in reducing cancer cell viability on their own, we have shown that the combined therapy can achieve near complete eradication (95.2% cell kill) of cancer cells even at an extremely low dose of 50 pM of NR-HS-Ce6 containing an equivalent of 7.67 μg mL-1 Au and 4.83 nM Ce6. This near complete cell kill at such a low dose has not been reported previously. The advantages of this nanoscale delivery system showcase the application of protein corona in cancer treatment instead of considering it as an undesirable biological artefact.

Understanding aggregation-based assays: nature of protein corona and number of epitopes on antigen matters

The development of assays that exploit aggregation of gold nanoparticles (NPs) has been widely studied for detection of biomolecules in diagnostics. These assays are often based on antibody–antigen interactions to mediate aggregation of NPs. However, the protein parameters underlying the performance of these assays are not well understood. In this study, we systematically examine how the nature of the protein corona on the NPs, formed from either antibody or antigen, and how the number of binding sites or epitopes on the antigen affect aggregation. We selected two small antigen proteins: 13 kDa recombinant dengue viral envelope domain III protein with a polyhistidine tag (DIII-His), and 19 kDa vascular endothelial growth factor A (VEGFA), to form protein corona around NPs and study the aggregation induced by their monoclonal and polyclonal antibodies. We then reciprocated the systems to form protein corona with the antibodies and compared the aggregation induced by the antigens. We showed that the nature of the protein corona matters, as the corona formed from antigens had lower limits of detection and elicited greater degrees of NP aggregation compared to the corona formed from antibodies. Furthermore, the number of epitopes on the antigen matters, as polyclonal antibodies, which target multiple epitopes on the antigen, were able to induce aggregation for both antigen- and antibody-corona systems. In contrast, monoclonal antibodies that target a single epitope on the antigens induced aggregation for the antigen-corona system only. Our results showed that an understanding of the antibody–antigen system is crucial for establishing guidelines for rational selection of proteins in the design of aggregation-based assays with NPs.

Dark-field circular depolarization optical coherence microscopy

Optical coherence microscopy (OCM) is a widely used structural imaging modality. To extend its application in molecular imaging, gold nanorods are widely used as contrast agents for OCM. However, they very often offer limited sensitivity as a result of poor signal to background ratio. Here we experimentally demonstrate that a novel OCM implementation based on dark-field circular depolarization detection can efficiently detect circularly depolarized signal from gold nanorods and at the same time efficiently suppress the background signals. This results into a significant improvement in signal to background ratio.

Polydopamine Nanoparticles Enhance Drug Release for Combined Photodynamic and Photothermal Therapy

Our study shows a facile two-step method which does not require the use of core templates to load a hydrophobic photosensitizer drug chlorin e6 (Ce6) within polydopamine (PDA) nanoparticles (NPs) while maintaining the intrinsic surface properties of PDA NPs. This structure is significantly different from hollow nanocapsules which are less stiff as they do not possess a core. To our knowledge, there exist no similar studies in the literature on drug loading within the polymer matrix of PDA NPs. We characterized the drug loading and release behavior of the photosensitizer Ce6 and demonstrated the therapeutic efficacy of the combined photodynamic (PDT) and photothermal therapy (PTT) from Ce6 and PDA, respectively, under a single wavelength of 665 nm irradiation on bladder cancer cells. We obtained a saturated loading amount of 14.2 ± 0.85 μM Ce6 in 1 nM PDA NPs by incubating 1 mg/mL dopamine solution with 140 μM of Ce6 for 20 h. The PDA NPs maintained colloidal stability in biological media, whereas the pi-pi (π-π) interaction between PDA and Ce6 enabled a release profile of the photosensitizer until day 5. Interestingly, loading of Ce6 in the polymer matrix of PDA NPs significantly enhanced the cell uptake because of endocytosis. An increased cell kill was observed with the combined PDT + PTT from 1 nM PDA-Ce6 compared to that with PTT alone with 1 nM PDA and PDT alone with 15 μM equivalent concentration of free Ce6. PDA-Ce6 NPs could be a promising PDT/PTT therapeutic agent for cancer therapy.

Gold nanorods in photomedicine

Abstract: This chapter discusses the applications of gold nanorods in photomedicine. Gold nanorods possess unique optical properties that allow them to be used in tandem with light-based therapeutic, imaging or sensing systems to detect and treat diseases. We begin the chapter with a general introduction to the synthesis, optical properties, surface functionalization, and biocompatibility of gold nanorods. Their use in photomedicine will then be presented in three major areas of applications, including therapy, therapeutic delivery, and probing of diseases through imaging and sensing. The principles behind these applications as well as some recent examples from scientific literature will be discussed to provide a good overview of the current state-of-the-art applications in each of these areas.