The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria.

Argininosuccinate lyase (ASL) is integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle. Inherited ASL deficiency causes argininosuccinic aciduria (ASA), a rare disease with hyperammonemia and NO deficiency. Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis. A neurodegenerative phenotype has been proposed in ASA. To better characterise this neurodegenerative phenotype in ASA, we conducted a retrospective study in six paediatric and adult metabolic centres in the UK in 2022. We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour. We analysed neuroimaging with diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) in an individual with ASA with movement disorders. We assessed conventional and DTI MRI alongside single photon emission computer tomography (SPECT) with dopamine analogue radionuclide 123 I-ioflupane, in Asl-deficient mice treated by hASL mRNA with normalised ureagenesis. Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia. Neuroimaging can show abnormal DTI features affecting both grey and white matter, preferentially basal ganglia. ASA mouse model with normalised ureagenesis did not recapitulate these DTI findings and showed normal 123 I-ioflupane SPECT and cerebral dopamine metabolomics. Altogether these findings support the pathophysiology of a late-onset movement disorder with cell-autonomous functional central catecholamine dysregulation but without or limited neurodegeneration of dopaminergic neurons, making these symptoms amenable to targeted therapy.

EGFR-targeted semiconducting polymer nanoparticles for photoacoustic imaging.

Semiconducting polymer nanoparticles (SPN), formulated from organic semiconducting polymers and lipids, show promise as exogenous contrast agents for photoacoustic imaging (PAI). To fully realise the potential of this class of nanoparticles for imaging and therapeutic applications, a broad range of active targeting strategies, where ligands specific to receptors on the target cells are displayed on the SPN surface, are urgently needed. In addition, effective strategies for quantifying the level of surface modification are also needed to support development of ligand-targeted SPN. In this paper, we have developed methods to prepare SPN bearing peptides targeted to Epidermal Growth Factor Receptors (EGFR), which are overexpressed at the surface of a wide variety of cancer cell types. In addition to fully characterising these targeted nanoparticles by standard methods (UV-visible, photoacoustic absorption, dynamic light scattering, zeta potential and SEM), we have developed a powerful new NMR method to determine the degree of conjugation and the number of targeting peptides attached to the SPN. Preliminary in vitro experiments with the colorectal cancer cell line LIM1215 indicated that the EGFR-targeting peptide conjugated SPN were either ineffective in delivering the SPN to the cells, or that the targeting peptide itself destabilised the formulation. This in reinforces the need for effective characterisation techniques to measure the surface accessibility of targeting ligands attached to nanoparticles.

Micro-CT acquisition and image processing to track and characterize pulmonary nodules in mice.

X-ray computed tomography is a reliable technique for the detection and longitudinal monitoring of pulmonary nodules. In preclinical stages of diagnostic or therapeutic development, the miniaturized versions of the clinical computed tomography scanners are ideally suited for carrying out translationally-relevant research in conditions that closely mimic those found in the clinic. In this Protocol, we provide image acquisition parameters optimized for low radiation dose, high-resolution and high-throughput computed tomography imaging using three commercially available micro-computed tomography scanners, together with a detailed description of the image analysis tools required to identify a variety of lung tumor types, characterized by specific radiological features. For each animal, image acquisition takes 4-8 min, and data analysis typically requires 10-30 min. Researchers with basic training in animal handling, medical imaging and software analysis should be able to implement this protocol across a wide range of lung cancer models in mice for investigating the molecular mechanisms driving lung cancer development and the assessment of diagnostic and therapeutic agents.

Image-Guided Magnetic Thermoseed Navigation and Tumor Ablation Using a Magnetic Resonance Imaging System.

Medical therapies achieve their control at expense to the patient in the form of a range of toxicities, which incur costs and diminish quality of life. Magnetic resonance navigation is an emergent technique that enables image-guided remote-control of magnetically labeled therapies and devices in the body, using a magnetic resonance imaging (MRI) system. Minimally INvasive IMage-guided Ablation (MINIMA), a novel, minimally invasive, MRI-guided ablation technique, which has the potential to avoid traditional toxicities, is presented. It comprises a thermoseed navigated to a target site using magnetic propulsion gradients generated by an MRI scanner, before inducing localized cell death using an MR-compatible thermoablative device. The authors demonstrate precise thermoseed imaging and navigation through brain tissue using an MRI system (0.3 mm), and they perform thermoablation in vitro and in vivo within subcutaneous tumors, with the focal ablation volume finely controlled by heating duration. MINIMA is a novel theranostic platform, combining imaging, navigation, and heating to deliver diagnosis and therapy in a single device.

Remote and Selective Control of Astrocytes by Magnetomechanical Stimulation.

Astrocytes play crucial and diverse roles in brain health and disease. The ability to selectively control astrocytes provides a valuable tool for understanding their function and has the therapeutic potential to correct dysfunction. Existing technologies such as optogenetics and chemogenetics require the introduction of foreign proteins, which adds a layer of complication and hinders their clinical translation. A novel technique, magnetomechanical stimulation (MMS), that enables remote and selective control of astrocytes without genetic modification is described here. MMS exploits the mechanosensitivity of astrocytes and triggers mechanogated Ca2+ and adenosine triphosphate (ATP) signaling by applying a magnetic field to antibody-functionalized magnetic particles that are targeted to astrocytes. Using purpose-built magnetic devices, the mechanosensory threshold of astrocytes is determined, a sub-micrometer particle for effective MMS is identified, the in vivo fate of the particles is established, and cardiovascular responses are induced in rats after particles are delivered to specific brainstem astrocytes. By eliminating the need for device implantation and genetic modification, MMS is a method for controlling astroglial activity with an improved prospect for clinical application than existing technologies.

Drug delivery, biodistribution and anti-EGFR activity: theragnostic nanoparticles for simultaneous in vivo delivery of tyrosine kinase inhibitors and kinase activity biosensors.

In vivo delivery of small molecule therapeutics to cancer cells, assessment of the selectivity of administration, and measuring the efficacity of the drug in question at the molecule level, are important ongoing challenges in developing new classes of cancer chemotherapeutics. One approach that has the potential to provide targeted delivery, tracking of biodistribution and readout of efficacy, is to use multimodal theragnostic nanoparticles to deliver the small molecule therapeutic. In this paper, we report the development of targeted theragnostic lipid/peptide/DNA lipopolyplexes. These simultaneously deliver an inhibitor of the EGFR tyrosine kinase, and plasmid DNA coding for a Crk-based biosensor, Picchu-X, which when expressed in the target cells can be used to quantify the inhibition of EGFR in vivo in a mouse colorectal cancer xenograft model. Reversible bioconjugation of a known analogue of the tyrosine kinase inhibitor Mo-IPQA to a cationic peptide, and co-formulation with peptides containing both EGFR-binding and cationic sequences, allowed for good levels of inhibitor encapsulation with targeted delivery to LIM1215 colon cancer cells. Furthermore, high levels of expression of the Picchu-X biosensor in the LIM1215 cells in vivo allowed us to demonstrate, using fluorescence lifetime microscopy (FLIM)-based biosensing, that EGFR activity can be successfully suppressed by the tyrosine kinase inhibitor, released from the lipopolyplexes. Finally, we measured the biodistribution of lipopolyplexes containing 125I-labelled inhibitors and were able to demonstrate that the lipopolyplexes gave significantly higher drug delivery to the tumors compared with free drug.

SARS-CoV-2 inhibition using a mucoadhesive, amphiphilic chitosan that may serve as an anti-viral nasal spray.

There are currently no cures for coronavirus infections, making the prevention of infections the only course open at the present time. The COVID-19 pandemic has been difficult to prevent, as the infection is spread by respiratory droplets and thus effective, scalable and safe preventive interventions are urgently needed. We hypothesise that preventing viral entry into mammalian nasal epithelial cells may be one way to limit the spread of COVID-19. Here we show that N-palmitoyl-N-monomethyl-N,N-dimethyl-N,N,N-trimethyl-6-O-glycolchitosan (GCPQ), a positively charged polymer that has been through an extensive Good Laboratory Practice toxicology screen, is able to reduce the infectivity of SARS-COV-2 in A549ACE2+ and Vero E6 cells with a log removal value of - 3 to - 4 at a concentration of 10-100 µg/ mL (p < 0.05 compared to untreated controls) and to limit infectivity in human airway epithelial cells at a concentration of 500 µg/ mL (p < 0.05 compared to untreated controls). In vivo studies using transgenic mice expressing the ACE-2 receptor, dosed nasally with SARS-COV-2 (426,000 TCID50/mL) showed a trend for nasal GCPQ (20 mg/kg) to inhibit viral load in the respiratory tract and brain, although the study was not powered to detect statistical significance. GCPQ's electrostatic binding to the virus, preventing viral entry into the host cells, is the most likely mechanism of viral inhibition. Radiolabelled GCPQ studies in mice show that at a dose of 10 mg/kg, GCPQ has a long residence time in mouse nares, with 13.1% of the injected dose identified from SPECT/CT in the nares, 24 h after nasal dosing. With a no observed adverse effect level of 18 mg/kg in rats, following a 28-day repeat dose study, clinical testing of this polymer, as a COVID-19 prophylactic is warranted.

Peritumoral Delivery of Docetaxel-TIPS Microparticles for Prostate Cancer Adjuvant Therapy.

Recurrence of prostate cancer after radical prostatectomy is a consequence of incomplete tumor resection. Systemic chemotherapy after surgery is associated with significant toxicity. Improved delivery methods for toxic drugs capable of targeting positive resection margins can reduce tumor recurrence and avoid their known toxicity. This study evaluates the effectiveness and toxicity of docetaxel (DTX) release from highly porous biodegradable microparticles intended for delivery into the tissue cavity created during radical prostatectomy to target residual tumor cells. The microparticles, composed of poly(dl-lactide-co-glycolide) (PLGA), are processed using thermally induced phase separation (TIPS) and loaded with DTX via antisolvent precipitation. Sustained drug release and effective toxicity in vitro are observed against PC3 human prostate cells. Peritumoral injection in a PC3 xenograft tumor model results in tumor growth inhibition equivalent to that achieved with intravenous delivery of DTX. Unlike intravenous delivery of DTX, implantation of DTX-TIPS microparticles is not accompanied by toxicity or elevated systemic levels of DTX in organ tissues or plasma. DTX-TIPS microparticles provide localized and sustained release of nontoxic therapeutic amounts of DTX. This may offer novel therapeutic strategies for improving management of patients with clinically localized high-risk disease requiring radical prostatectomy and other solid cancers at high risk of positive resection margins.

Development of [18F]AldoView as the First Highly Selective Aldosterone Synthase PET Tracer for Imaging of Primary Hyperaldosteronism.

The purpose of this study was to synthesize a fluorine-18 labeled, highly selective aldosterone synthase (hCYP11B2) inhibitor, [18F]AldoView, and to assess its potential for the detection of aldosterone-producing adenomas (APAs) with positron emission tomography in patients with primary hyperaldosteronism (PHA). Using dibenzothiophene sulfonium salt chemistry, [18F]AldoView was obtained in high radiochemical yield in one step from [18F]fluoride. In mice, the tracer showed a favorable pharmacokinetic profile, including rapid distribution and clearance. Imaging in the adrenal tissue from patients with PHA revealed diffuse binding patterns in the adrenal cortex, avid binding in some adenomas, and "hot spots" consistent with aldosterone-producing cell clusters. The binding pattern was in good visual agreement with the antibody staining of hCYP11B2 and distinguished areas with normal and excessive hCYP11B2 expression. Taken together, [18F]AldoView is a promising tracer for the detection of APAs in patients with PHA.

Image-guided Raman spectroscopy probe-tracking for tumor margin delineation.

SIGNIFICANCE: Tumor detection and margin delineation are essential for successful tumor resection. However, postsurgical positive margin rates remain high for many cancers. Raman spectroscopy has shown promise as a highly accurate clinical spectroscopic diagnostic modality, but its margin delineation capabilities are severely limited by the need for pointwise application. AIM: We aim to extend Raman spectroscopic diagnostics and develop a multimodal computer vision-based diagnostic system capable of both the detection and identification of suspicious lesions and the precise delineation of disease margins. APPROACH: We first apply visual tracking of a Raman spectroscopic probe to achieve real-time tumor margin delineation. We then combine this system with protoporphyrin IX fluorescence imaging to achieve fluorescence-guided Raman spectroscopic margin delineation. RESULTS: Our system enables real-time Raman spectroscopic tumor margin delineation for both ex vivo human tumor biopsies and an in vivo tumor xenograft mouse model. We then further demonstrate that the addition of protoporphyrin IX fluorescence imaging enables fluorescence-guided Raman spectroscopic margin delineation in a tissue phantom model. CONCLUSIONS: Our image-guided Raman spectroscopic probe-tracking system enables tumor margin delineation and is compatible with both white light and fluorescence image guidance, demonstrating the potential for our system to be developed toward clinical tumor resection surgeries.

Potential of Magnetic Hyperthermia to Stimulate Localized Immune Activation.

Magnetic hyperthermia (MH) harnesses the heat-releasing properties of superparamagnetic iron oxide nanoparticles (SPIONs) and has potential to stimulate immune activation in the tumor microenvironment whilst sparing surrounding normal tissues. To assess feasibility of localized MH in vivo, SPIONs are injected intratumorally and their fate tracked by Zirconium-89-positron emission tomography, histological analysis, and electron microscopy. Experiments show that an average of 49% (21-87%, n = 9) of SPIONs are retained within the tumor or immediately surrounding tissue. In situ heating is subsequently generated by exposure to an externally applied alternating magnetic field and monitored by thermal imaging. Tissue response to hyperthermia, measured by immunohistochemical image analysis, reveals specific and localized heat-shock protein expression following treatment. Tumor growth inhibition is also observed. To evaluate the potential effects of MH on the immune landscape, flow cytometry is used to characterize immune cells from excised tumors and draining lymph nodes. Results show an influx of activated cytotoxic T cells, alongside an increase in proliferating regulatory T cells, following treatment. Complementary changes are found in draining lymph nodes. In conclusion, results indicate that biologically reactive MH is achievable in vivo and can generate localized changes consistent with an anti-tumor immune response.

Integrated photodynamic Raman theranostic system for cancer diagnosis, treatment, and post-treatment molecular monitoring.

Theranostics, the combination of diagnosis and therapy, has long held promise as a means to achieving personalised precision cancer treatments. However, despite its potential, theranostics has yet to realise significant clinical translation, largely due the complexity and overriding toxicity concerns of existing theranostic nanoparticle strategies. Methods: Here, we present an alternative nanoparticle-free theranostic approach based on simultaneous Raman spectroscopy and photodynamic therapy (PDT) in an integrated clinical platform for cancer theranostics. Results: We detail the compatibility of Raman spectroscopy and PDT for cancer theranostics, whereby Raman spectroscopic diagnosis can be performed on PDT photosensitiser-positive cells and tissues without inadvertent photosensitiser activation/photobleaching or impaired diagnostic capacity. We further demonstrate that our theranostic platform enables in vivo tumour diagnosis, treatment, and post-treatment molecular monitoring in real-time. Conclusion: This system thus achieves effective theranostic performance, providing a promising new avenue towards the clinical realisation of theranostics.

Intratumoral IL-12 delivery empowers CAR-T cell immunotherapy in a pre-clinical model of glioblastoma.

Glioblastoma multiforme (GBM) is the most common and aggressive form of primary brain cancer, for which effective therapies are urgently needed. Chimeric antigen receptor (CAR)-based immunotherapy represents a promising therapeutic approach, but it is often impeded by highly immunosuppressive tumor microenvironments (TME). Here, in an immunocompetent, orthotopic GBM mouse model, we show that CAR-T cells targeting tumor-specific epidermal growth factor receptor variant III (EGFRvIII) alone fail to control fully established tumors but, when combined with a single, locally delivered dose of IL-12, achieve durable anti-tumor responses. IL-12 not only boosts cytotoxicity of CAR-T cells, but also reshapes the TME, driving increased infiltration of proinflammatory CD4+ T cells, decreased numbers of regulatory T cells (Treg), and activation of the myeloid compartment. Importantly, the immunotherapy-enabling benefits of IL-12 are achieved with minimal systemic effects. Our findings thus show that local delivery of IL-12 may be an effective adjuvant for CAR-T cell therapy for GBM.

Multi-modal imaging probe for assessing the efficiency of stem cell delivery to orthotopic breast tumours.

Stem cells have been utilised as anti-cancer agents due to their ability to home to and integrate within tumours. Methods to augment stem cell homing to tumours are being investigated with the goal of enhancing treatment efficacy. However, it is currently not possible to evaluate both cell localisation and cell viability after engraftment, hindering optimisation of therapy. In this study, luciferase-expressing human adipocyte-derived stem cells (ADSCs) were incubated with Indium-111 radiolabelled iron oxide nanoparticles to produce cells with tri-modal imaging capabilities. ADSCs were administered intravenously (IV) or intracardially (IC) to mice bearing orthotopic breast tumours. Cell fate was monitored using bioluminescence imaging (BLI) as a measure of cell viability, magnetic resonance imaging (MRI) for cell localisation and single photon emission computer tomography (SPECT) for cell quantification. Serial monitoring with multi-modal imaging showed the presence of viable ADSCs within tumours as early as 1-hour post IC injection and the percentage of ADSCs within tumours to be 2-fold higher after IC than IV. Finally, histological analysis was used to validate engraftment of ADSC within tumour tissue. These findings demonstrate that multi-modal imaging can be used to evaluate the efficiency of stem cell delivery to tumours and that IC cell administration is more effective for tumour targeting.

Lung delivery of MSCs expressing anti-cancer protein TRAIL visualised with 89Zr-oxine PET-CT.

BACKGROUND: MSCTRAIL is a cell-based therapy consisting of human allogeneic umbilical cord-derived MSCs genetically modified to express the anti-cancer protein TRAIL. Though cell-based therapies are typically designed with a target tissue in mind, delivery is rarely assessed due to a lack of translatable non-invasive imaging approaches. In this preclinical study, we demonstrate 89Zr-oxine labelling and PET-CT imaging as a potential clinical solution for non-invasively tracking MSCTRAIL biodistribution. Future implementation of this technique should improve our understanding of MSCTRAIL during its evaluation as a therapy for metastatic lung adenocarcinoma. METHODS: MSCTRAIL were radiolabelled with 89Zr-oxine and assayed for viability, phenotype, and therapeutic efficacy post-labelling. PET-CT imaging of 89Zr-oxine-labelled MSCTRAIL was performed in a mouse model of lung cancer following intravenous injection, and biodistribution was confirmed ex vivo. RESULTS: MSCTRAIL retained the therapeutic efficacy and MSC phenotype in vitro at labelling amounts up to and above those required for clinical imaging. The effect of 89Zr-oxine labelling on cell proliferation rate was amount- and time-dependent. PET-CT imaging showed delivery of MSCTRAIL to the lungs in a mouse model of lung cancer up to 1 week post-injection, validated by in vivo bioluminescence imaging, autoradiography, and fluorescence imaging on tissue sections. CONCLUSIONS: 89Zr-oxine labelling and PET-CT imaging present a potential method of evaluating the biodistribution of new cell therapies in patients, including MSCTRAIL. This offers to improve understanding of cell therapies, including mechanism of action, migration dynamics, and inter-patient variability.

Stem cell delivery to kidney via minimally invasive ultrasound-guided renal artery injection in mice.

Cell-based therapies are promising treatments for various kidney diseases. However, the major hurdle in initiating therapeutic responses is the inefficiency of injection routes to deliver cells to the kidney parenchyma. Systemic injection, such as intravenous injection only delivers a small proportion of cells to the kidney. Whereas direct delivery, such as renal artery injection requires surgical procedures. A minimally invasive renal artery injection was therefore developed to enhance cell delivery to kidney. In this study, luciferase expressing human adipocyte derived stem cells (ADSC) were labelled with gold nanorods (GNR) and injected into the renal artery using ultrasound guidance. The ADSCs were tracked using bioluminescence and photoacoustic imaging serially over 7 days. Imaging confirmed that the majority of signal was within the kidney, indicative of successful injection and that the cells remained viable for 3 days. Histology showed co-localization of GNRs with ADSC staining throughout the kidney with no indication of injury caused by injection. These findings demonstrate that ultrasound-guided renal artery injection is feasible in mice and can successfully deliver a large proportion of cells which are retained within the kidney for 3 days. Therefore, the techniques developed here will be useful for optimising cell therapy in kidney diseases.

In vivo photoacoustic imaging of a nonfluorescent E2 crimson genetic reporter in mammalian tissues.

SIGNIFICANCE: Green-fluorescent protein (GFP)-like fluorescent proteins are used extensively as genetic reporters in fluorescence imaging due to their distinctive ability to form chromophores independent of external enzymes or cofactors. However, their use for photoacoustic (PA) imaging has not been demonstrated in mammalian tissues because they possess low PA signal generation efficiency in their native state. By engineering them to become nonfluorescent (NF), their PA generation efficiency was increased. This enabled the generation of in vivo contrast in mice, making it possible for GFP-like proteins to be used as PA genetic reporters in mammalian tissues. AIM: The aim was to develop a darkened GFP-like protein reporter by modifying E2 crimson fluorescent protein (FP) in order to generate NF mutant proteins with high PA signal generation efficiency for in vivo imaging. APPROACH: The absorbance, fluorescence, and PA amplitude spectra of purified protein solutions of the FP and engineered NF mutants were measured in order to identify the mutant with the highest PA signal generation efficiency. This mutant, referred to as NFA, and the native FP were then stably expressed in LS174T human colorectal tumor cells using a retroviral vector and tested for photostability under continuous pulsed illumination. To demonstrate the improvement in PA signal generation in vivo, cells expressing the FP and NFA mutant were injected subcutaneously in mice and imaged using a Fabry-Perot based PA scanner. RESULTS: The NF mutants of E2 crimson exhibited fluorescence that was 2 orders of magnitude lower than the FP and a higher PA signal generation efficiency; the NFA-generated PA signal was approximately three times higher than the FP. Tumor cells expressing the NFA mutant provided sufficient image contrast to be visualized in vivo against a background of strong vascular contrast, whereas the FP-expressing cells did not generate visible contrast. CONCLUSION: A GFP-like protein has been demonstrated as a genetic reporter for PA imaging in mammalian tissue for the first time. This was achieved by a mutation, which darkened the FP and increased the PA signal generation efficiency. The approach taken suggests that GFP-like proteins could be a promising addition to the current cohort of genetic reporters available for in vivo PA imaging.

Radio-metal cross-linking of alginate hydrogels for non-invasive in vivo imaging.

Alginate hydrogels are cross-linked polymers with high water content, tuneable chemical and material properties, and a range of biomedical applications including drug delivery, tissue engineering, and cell therapy. However, their similarity to soft tissue often renders them undetectable within the body using conventional bio-medical imaging techniques. This leaves much unknown about their behaviour in vivo, posing a challenge to therapy development and validation. To address this, we report a novel, fast, and simple method of incorporating the nuclear imaging radio-metal 111In into the structure of alginate hydrogels by utilising its previously-undescribed capacity as an ionic cross-linking agent. This enabled non-invasive in vivo nuclear imaging of hydrogel delivery and retention across the whole body, over time, and across a range of model therapies including: nasal and oral drug delivery, stem cell transplantation, and cardiac tissue engineering. This information will facilitate the development of novel therapeutic hydrogel formulations, encompassing alginate, across disease categories.

Imaging of X-Ray-Excited Emissions from Quantum Dots and Biological Tissue in Whole Mouse.

Optical imaging in clinical and preclinical settings can provide a wealth of biological information, particularly when coupled with targetted nanoparticles, but optical scattering and absorption limit the depth and resolution in both animal and human subjects. Two new hybrid approaches are presented, using the penetrating power of X-rays to increase the depth of optical imaging. Foremost, we demonstrate the excitation by X-rays of quantum-dots (QD) emitting in the near-infrared (NIR), using a clinical X-ray system to map the distribution of QDs at depth in whole mouse. We elicit a clear, spatially-resolved NIR signal from deep organs (brain, liver and kidney) with short (1 second) exposures and tolerable radiation doses that will permit future in vivo applications. Furthermore, X-ray-excited endogenous emission is also detected from whole mouse. The use of keV X-rays to excite emission from QDs and tissue represent novel biomedical imaging technologies, and exploit emerging QDs as optical probes for spatial-temporal molecular imaging at greater depth than previously possible.