Sukanta Kamila

Anion sensing with luminescent quantum dots - A modular approach based on the photoinduced electron transfer (PET) mechanism

A CdSe–ZnS quantum dot (QD) has been surface functionalised with 1-(2-mercapto-ethyl)-3-phenyl-thiourea in the fluorophore–spacer–receptor format typical of Photoinduced Electron Transfer (PET) based organic dye sensors. The resulting QD conjugate was tested for selectivity toward the tetrabutylammonium salts of fluoride, chloride, bromide, hydrogen sulfate and acetate. Addition of fluoride, chloride and acetate ions resulted in an approximate 90% quenching of the original fluorescence intensity, while bromide and hydrogen sulfate had almost no effect. The observed quench was attributed to an increase in the reduction potential of the receptor upon anion binding resulting in an increase in PET from the excited QD to the receptor and a concomitant reduction in fluorescence intensity. The selectivity and sensitivity were comparable to an analagous organic dye based sensor where a similar receptor was bound to an anthracene fluorophore. Thus a modular approach is evident where a receptor used in an organic dye based sensor can be adapted and successfully used with QD’s.

Luminescent Detection of ATP in Aqueous Solution Using Positively Charged CdSe–ZnS Quantum Dots

Commercially available CdSe–ZnS Quantum Dots (QDs) have been modified by exchanging the hydrophobic surface ligands with (2-mercaptoethyl)-trimethylammonium chloride. The resulting water soluble conjugate was titrated with solutions of adenosine triphosphate (ATP), adenosine diphosphate, adenosine monophosphate, guanosine triphosphate (GTP), guanosine diphosphate and guanosine monophosphate in 0.01xa0M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 7.4). A strong fluorescence quench of about 80% was observed for ATP, a quench of 25% was observed for GTP while the others had virtually no effect. The quenching effect of ATP and GTP was attributed to the high negative charge density associated with these substrate’s resulting in a strong attraction to the QD surface enabling them to engage in electron transfer with the excited QD. The lack of fluorescence quenching associated with the other nucleotides was most likely due to their reduced charge density resulting in a lower affinity for the QD surface.

Combined sonodynamic and antimetabolite therapy for the improved treatment of pancreatic cancer using oxygen loaded microbubbles as a delivery vehicle

In this manuscript we describe the preparation of an oxygen-loaded microbubble (O2MB) platform for the targeted treatment of pancreatic cancer using both sonodynamic therapy (SDT) and antimetabolite therapy. O2MB were prepared with either the sensitiser Rose Bengal (O2MB-RB) or the antimetabolite 5-fluorouracil (O2MB-5FU) attached to the microbubble (MB) surface. The MB were characterised with respect to size, physical stability and oxygen retention. A statistically significant reduction in cell viability was observed when three different pancreatic cancer cell lines (BxPc-3, MIA PaCa-2 and PANC-1), cultured in an anaerobic cabinet, were treated with both SDT and antimetabolite therapy compared to either therapy alone. In addition, a statistically significant reduction in tumour growth was also observed when ectopic human xenograft BxPC-3 tumours in SCID mice were treated with the combined therapy compared to treatment with either therapy alone. These results illustrate not only the potential of combined SDT/antimetabolite therapy as a stand alone treatment option in pancreatic cancer, but also the capability of O2-loaded MBs to deliver O2 to the tumour microenvironment in order to enhance the efficacy of therapies that depend on O2 to mediate their therapeutic effect. Furthermore, the use of MBs to facilitate delivery of O2 as well as the sensitiser/antimetabolite, combined with the possibility to activate the sensitiser using externally applied ultrasound, provides a more targeted approach with improved efficacy and reduced side effects when compared with conventional systemic administration of antimetabolite drugs alone.

Diagnostic and Therapeutic Applications of Quantum Dots in Nanomedicine.

The interest in Quantum Dots as a class of nanomaterials has grown considerably since their discovery by Ekimov and Efros in the early 1980s. Although this early work focussed primarily on CdSe-based nanocrystals, the field has now expanded to include various classes of nanoparticles with different types of core, shell or passivation chemistry. Such differences can have a profound effect on the optical properties and potential biocompatibility of the resulting constructs. Although QDs have predominantly been used for imaging and sensing applications, more examples of their use as therapeutics are beginning to emerge. In this chapter we discuss the progress made over the past decade in developing QDs for imaging and therapeutic applications.

A folic acid labelled carbon quantum dot-protoporphryin IX conjugate for use in folate receptor targeted two-photon excited photodynamic therapy

Folic acid (FA) has been used as a molecular targeting strategy to improve the specificity of a CQD-protoporphyrin IX (CQD-PPIX) conjugate to folate receptor positive (FR+) HeLa cells for use in two-photon excited Photodynamic Therapy (TPE-PDT). FA was covalently attached to the CQD-PPIX conjugate to form a FA-CQD-PPIX conjugate. The uptake of the FA-CQD-PPIX conjugate in FR+ HeLa cells was shown to be 7 times greater than the CQD-PPIX conjugate, while both conjugates showed a similar uptake in FR negative (FR-) HT-47 cells. TPE-PDT experiments, using HeLa cells as a target, revealed a 30% improved cytotoxicity for cells treated with the FA-CQD-PPIX conjugate and TPE compared to controls treated with the CQD-PPIX conjugate and TPE. Collectively, these results suggest the presence of FA can facilitate targeting of CQD-sensitiser conjugates to FR+ cells resulting in an improved PDT effect.

Determination of zinc in aqueous solution using CdSe/ZnS quantum dots functionalised with [carboxymethyl-(4-mercapto-phenyl)-amino]-acetate

CdSe/ZnS quantum dots functionalised with [Carboxymethyl-(4-mercapto-phenyl)-amino]-acetate displayed selectivity for Zn2+ ion when tested against a range of other commonly available metal ions in buffered aqueous solution (pH 7.0 ± 0.1). The probe displayed an enhancement in its fluorescence intensity upon addition of Zn2+ attributed to a cancellation of a photoinduced electron transfer process from the bound receptor to the excited quantum dot that otherwise led to non-radiative decay. Good linearity was established for Zn2+ in the 0.2 to 5.0 mM range.

A new class of fluorescent chemosensors based on the β-aminobisphosphonate receptor

The photophysical properties of a range of fluorescent sensors with β-aminobisphosphonate receptors have been studied. The compounds were designed according to the fluorophore–spacer–receptor format of photoinduced electron transfer-based sensors. The sensors displayed unusual fluorescence intensity–pH profiles that were attributed to a receptor–fluorophore H-bonding interaction that resulted in a quenching of fluorescence. The number of receptors and the nature of the fluorophore were both shown to have an effect on the pH profiles of the sensors. In addition, compound 1 was also shown to be selective for Cu2+ ions, in water at pH 7.4 with sensitivity in the micromolar range.

Gemcitabine loaded microbubbles for targeted chemo-sonodynamic therapy of pancreatic cancer.

ABSTRACT Pancreatic cancer remains one of the most lethal forms of cancer with a 10‐year survival of <1%. With little improvement in survival rates observed in the past 40years, there is a significant need for new treatments or more effective strategies to deliver existing treatments. The antimetabolite gemcitabine (Gem) is the most widely used form of chemotherapy for pancreatic cancer treatment, but is known to produce significant side effects when administered systemically. We have previously demonstrated the benefit of combined chemo‐sonodynamic therapy (SDT), delivered using oxygen carrying microbubbles (O2MB), as a targeted treatment for pancreatic cancer in a murine model of the disease. In this manuscript, we report the preparation of a biotin functionalised Gem ligand for attachment to O2MBs (O2MB‐Gem). We demonstrate the effectiveness of chemo‐sonodynamic therapy following ultrasound‐targeted‐microbubble‐destruction (UTMD) of the O2MB‐Gem and a Rose Bengal loaded O2MB (O2MB‐RB) as a targeted treatment for pancreatic cancer. Specifically, UTMD using the O2MB‐Gem and O2MB‐RB conjugates reduced the viability of MIA PaCa‐2, PANC‐1, BxPC3 and T110299 pancreatic cancer cells by >60% (p<0.001) and provided significant tumour growth delay (>80%, p<0.001) compared to untreated animals when human xenograft MIA PaCa‐2 tumours were treated in SCID mice. The toxicity of the O2MB‐Gem conjugate was also determined in healthy non‐tumour bearing MF1 mice and revealed no evidence of renal or hepatic damage. Therefore, the results presented in this manuscript suggest that chemo‐sonodynamic therapy using the O2MB‐Gem and O2MB‐RB conjugates, is potentially an effective targeted and safe treatment modality for pancreatic cancer.

Magnetically responsive microbubbles as delivery vehicles for targeted sonodynamic and antimetabolite therapy of pancreatic cancer.

Magnetically responsive microbubbles (MagMBs), consisting of an oxygen gas core and a phospholipid coating functionalised with Rose Bengal (RB) and/or 5-fluorouracil (5-FU), were assessed as a delivery vehicle for the targeted treatment of pancreatic cancer using combined antimetabolite and sonodynamic therapy (SDT). MagMBs delivering the combined 5-FU/SDT treatment produced a reduction in cell viability of over 50% when tested against a panel of four pancreatic cancer cell lines in vitro. Intravenous administration of the MagMBs to mice bearing orthotopic human xenograft BxPC-3 tumours yielded a 48.3% reduction in tumour volume relative to an untreated control group (p<0.05) when the tumour was exposed to both external magnetic and ultrasound fields during administration of the MagMBs. In contrast, application of an external ultrasound field alone resulted in a 27% reduction in tumour volume. In addition, activated caspase and BAX protein levels were both observed to be significantly elevated in tumours harvested from animals treated with the MagMBs in the presence of magnetic and ultrasonic fields when compared to expression of those proteins in tumours from either the control or ultrasound field only groups (p<0.05). These results suggest MagMBs have considerable potential as a platform to enable the targeted delivery of combined sonodynamic/antimetabolite therapy in pancreatic cancer.

A low affinity nanoparticle based fluorescent ratiometric probe for the determination of Zn(II) concentrations in living cells

A ratiometric polymeric fluorescent probe for Zn(II) was developed comprising a Zn(II) responsive naphthalimide sensing unit and a Zn(II) insensitive rhodamine based calibration fluorophore attached to a common poly(methyl methacrylate) backbone. The Zn(II) responsive unit was designed to operate according to the photoinduced electron transfer (PET) mechanism with the naphthalimide fluorescence intensity increasing with increasing Zn(II) concentration. The amphiphilic polymeric probe was found to self-assemble in aqueous solution to generate nanoparticles with a hydrodynamic diameter of 10.61 ± 7.61 nm. Good selectivity for Zn(II) was observed when tested against a range of physiological relevant cations and excellent linearity (R2 = 0.99) was demonstrated in the 0–5.0 mM Zn(II) range when the ratiometric intensity (I527/I580) was plotted as a function of Zn(II) concentration. The probe was also capable of discriminating between resting and high Zn(II) levels in living cells using confocal fluorescence microscopy and exhibited no evidence of cellular toxicity. Combined, these results highlight the potential of the nanoparticle probe as a low-affinity ratiometric sensor for Zn(II) compatible with use in living cells.