3D Acoustic Wave Sparsely Activated Localization Microscopy With Phase Change Contrast Agents.

OBJECTIVE: The aim of this study is to demonstrate 3-dimensional (3D) acoustic wave sparsely activated localization microscopy (AWSALM) of microvascular flow in vivo using phase change contrast agents (PCCAs). MATERIALS AND METHODS: Three-dimensional AWSALM using acoustically activable PCCAs was evaluated on a crossed tube microflow phantom, the kidney of New Zealand White rabbits, and the brain of C57BL/6J mice through intact skull. A mixture of C 3 F 8 and C 4 F 10 low-boiling-point fluorocarbon gas was used to generate PCCAs with an appropriate activation pressure. A multiplexed 8-MHz matrix array connected to a 256-channel ultrasound research platform was used for transmitting activation and imaging ultrasound pulses and recording echoes. The in vitro and in vivo echo data were subsequently beamformed and processed using a set of customized algorithms for generating 3D super-resolution ultrasound images through localizing and tracking activated contrast agents. RESULTS: With 3D AWSALM, the acoustic activation of PCCAs can be controlled both spatially and temporally, enabling contrast on demand and capable of revealing 3D microvascular connectivity. The spatial resolution of the 3D AWSALM images measured using Fourier shell correlation is 64 µm, presenting a 9-time improvement compared with the point spread function and 1.5 times compared with half the wavelength. Compared with the microbubble-based approach, more signals were localized in the microvasculature at similar concentrations while retaining sparsity and longer tracks in larger vessels. Transcranial imaging was demonstrated as a proof of principle of PCCA activation in the mouse brain with 3D AWSALM. CONCLUSIONS: Three-dimensional AWSALM generates volumetric ultrasound super-resolution microvascular images in vivo with spatiotemporal selectivity and enhanced microvascular penetration.

Improved therapeutic antibody delivery to xenograft tumors using cavitation nucleated by gas-entrapping nanoparticles.

Aims: Testing ultrasound-mediated cavitation for enhanced delivery of the therapeutic antibody cetuximab to tumors in a mouse model. Methods: Tumors with strong EGF receptor expression were grown bilaterally. Cetuximab was coadministered intravenously with cavitation nuclei, consisting of either the ultrasound contrast agent Sonovue or gas-stabilizing nanoscale SonoTran Particles. One of the two tumors was exposed to focused ultrasound. Passive acoustic mapping localized and monitored cavitation activity. Both tumors were then excised and cetuximab concentration was quantified. Results: Cavitation increased tumoral cetuximab concentration. When nucleated by Sonovue, a 2.1-fold increase (95% CI 1.3- to 3.4-fold) was measured, whereas SonoTran Particles gave a 3.6-fold increase (95% CI 2.3- to 5.8-fold). Conclusions: Ultrasound-mediated cavitation, especially when nucleated by nanoscale gas-entrapping particles, can noninvasively increase site-specific delivery of therapeutic antibodies to solid tumors.

Investigation of the Acoustic Vaporization Threshold of Lipid-Coated Perfluorobutane Nanodroplets Using Both High-Speed Optical Imaging and Acoustic Methods.

A combination of ultrahigh-speed optical imaging (5 × 106 frames/s), B-mode ultrasound and passive cavitation detection was used to study the vaporization process and determine both the acoustic droplet vaporization (ADV) and inertial cavitation (IC) thresholds of phospholipid-coated perfluorobutane nanodroplets (PFB NDs, diameter = 237 ± 16 nm). PFB NDs have not previously been studied with ultrahigh-speed imaging and were observed to form individual microbubbles (1-10 µm) within two to three cycles and subsequently larger bubble clusters (10-50 µm). The ADV and IC thresholds did not statistically significantly differ and decreased with increasing pulse length (20-20,000 cycles), pulse repetition frequency (1-100 Hz), concentration (108-1010 NDs/mL), temperature (20°C-45°C) and decreasing frequency (1.5-0.5 MHz). Overall, the results indicate that at frequencies of 0.5, 1.0 and 1.5 MHz, PFB NDs can be vaporized at moderate peak negative pressures (<2.0 MPa), pulse lengths and pulse repetition frequencies. This finding is encouraging for the use of PFB NDs as cavitation agents, as these conditions are comparable to those required to achieve therapeutic effects with microbubbles, unlike those reported for higher-boiling-point NDs. The differences between the optically and acoustically determined ADV thresholds, however, suggest that application-specific thresholds should be defined according to the biological/therapeutic effect of interest.

Polymer stealthing and mucin-1 retargeting for enhanced pharmacokinetics of an oncolytic vaccinia virus.

Vaccinia virus (VV) is a powerful tool for cancer treatment with the potential for tumor tropism, efficient cell-to-cell spread, rapid replication in cancer cells, and stimulation of anti-tumor immunity. It has a well-defined safety profile and is being assessed in late-stage clinical trials. However, VV clinical utility is limited by rapid bloodstream neutralization and poor penetration into tumors. These factors have often restricted its route of delivery to intratumoral or intrahepatic artery injection and may impede repeat dosing. Chemical stealthing improves the pharmacokinetics of non-enveloped viruses, but it has not yet been applied to enveloped viruses such as VV. In the present study, amphiphilic polymer was used to coat VV, leading to reduced binding of a neutralizing anti-VV antibody (81.8% of polymer-coated VV [PCVV] staining positive versus 97.1% of VV [p = 0.0038]). Attachment of anti-mucin-1 (aMUC1) targeting antibody, to give aMUC1-PCVV, enabled binding of the construct to MUC1. In high MUC1 expressing CAPAN-2 cells, infection with PCVV was reduced compared to VV, while infection was restored with aMUC1-PCVV. Pharmacokinetics of aMUC1-PCVV, PCVV, and VV were evaluated. After intravenous (i.v.) injection of 1 × 108 viral genomes (VG) or 5 × 108 VG, circulation time for PCVV and aMUC1-PCVV was increased, with ~5-fold higher circulating dose at 5 min versus VV.

Evaluation of Loading Strategies to Improve Tumor Uptake of Gemcitabine in a Murine Orthotopic Bladder Cancer Model Using Ultrasound and Microbubbles.

In this study we compared three different microbubble-based approaches to the delivery of a widely used chemotherapy drug, gemcitabine: (i) co-administration of gemcitabine and microbubbles (Gem+MB); (ii) conjugates of microbubbles and gemcitabine-loaded liposomes (GemlipoMB); and (iii) microbubbles with gemcitabine directly bound to their surfaces (GembioMB). Both in vitro and in vivo investigations were carried out, respectively, in the RT112 bladder cancer cell line and in a murine orthotopic muscle-invasive bladder cancer model. The in vitro (in vivo) ultrasound exposure conditions were a 1 (1.1) MHz centre frequency, 0.07 (1.0) MPa peak negative pressure, 3000 (20,000) cycles and 100 (0.5) Hz pulse repetition frequency. Ultrasound exposure produced no significant increase in drug uptake either in vitro or in vivo compared with the drug-only control for co-administered gemcitabine and microbubbles. In vivo, GemlipoMB prolonged the plasma circulation time of gemcitabine, but only GembioMB produced a statistically significant increase in cleaved caspase 3 expression in the tumor, indicative of gemcitabine-induced apoptosis.

Ultrasound-Mediated Gemcitabine Delivery Reduces the Normal-Tissue Toxicity of Chemoradiation Therapy in a Muscle-Invasive Bladder Cancer Model.

PURPOSE: Chemoradiation therapy is the standard of care in muscle-invasive bladder cancer (MIBC). Although agents such as gemcitabine can enhance tumor radiosensitivity, their side effects can limit patient eligibility and treatment efficacy. This study investigates ultrasound and microbubbles for targeting gemcitabine delivery to reduce normal-tissue toxicity in a murine orthotopic MIBC model. MATERIALS AND METHODS: CD1-nude mice were injected orthotopically with RT112 bladder tumor cells. Conventional chemoradiation involved injecting gemcitabine (10 mg/kg) before 6 Gy targeted irradiation of the bladder area using the Small Animal Radiation Research Platform (SARRP). Ultrasound-mediated gemcitabine delivery (10 mg/kg gemcitabine) involved either coadministration of microbubbles with gemcitabine or conjugating gemcitabine onto microbubbles followed by exposure to ultrasound (1.1 MHz center frequency, 1 MPa peak negative pressure, 1% duty cycle, and 0.5 Hz pulse repetition frequency) before SARRP irradiation. The effect of ultrasound and microbubbles alone was also tested. Tumor volumes were measured by 3D ultrasound imaging. Acute normal-tissue toxicity from 12 Gy to the lower bowel area was assessed using an intestinal crypt assay in mice culled 3.75 days posttreatment. RESULTS: A significant delay in tumor growth was observed with conventional chemoradiation therapy and both microbubble groups (P < .05 compared with the radiation-only group). Transient weight loss was seen in the microbubble groups, which resolved within 10 days posttreatment. A positive correlation was found between weight loss on day 3 posttreatment and tumor growth delay (P < .05; R2 = 0.76). In contrast with conventional chemoradiation therapy, ultrasound-mediated drug delivery methods did not exacerbate the acute intestinal toxicity using the crypt assay. CONCLUSIONS: Ultrasound and microbubbles offer a promising new approach for improving chemoradiation therapy for muscle-invasive bladder cancer, maintaining a delay in tumor growth but with reduced acute intestinal toxicity compared with conventional chemoradiation therapy.

Combining sonodynamic therapy with chemoradiation for the treatment of pancreatic cancer.

Treatment options for patients with pancreatic cancer are limited and survival prospects have barely changed over the past 4 decades. Chemoradiation treatment (CRT) has been used as neoadjuvant therapy in patients with borderline resectable disease to reduce tumour burden and increase the proportion of patients eligible for surgery. Antimetabolite drugs such as gemcitabine and 5-fluorouracil are known to sensitise pancreatic tumours to radiation treatment. Likewise, photodynamic therapy (PDT) has also been shown to enhance the effect of radiation therapy. However, PDT is limited to treating superficial lesions due to the attenuation of light by tissue. The ability of the related technique, sonodynamic therapy (SDT), to enhance CRT was investigated in two murine models of pancreatic cancer (PSN-1 and BxPC-3) in this study. SDT uses low intensity ultrasound to activate an otherwise non-toxic sensitiser, generating toxic levels of reactive oxygen species (ROS) locally. It is applicable to greater target depths than PDT due to the ability of ultrasound to propagate further than light in tissue. Both CRT and the combination of CRT plus SDT delayed tumour growth in the two tumour models. In the PSN-1 model, but not the BxPC-3 model, the combination treatment caused an increase in survival relative to CRT alone (p = 0.038). The improvement in survival conferred by the addition of SDT in this model may be related to differences in tumour architecture between the two models. MRI and US images showed that PSN-1 tumours were less well perfused and vascularised than BxPC-3 tumours. This poor vascularisation may explain why PSN-1 tumours were more susceptible to the effects of vascular damage exerted by SDT treatment.

Acute Immune Signatures and Their Legacies in Severe Acute Respiratory Syndrome Coronavirus-2 Infected Cancer Patients.

Given the immune system's importance for cancer surveillance and treatment, we have investigated how it may be affected by SARS-CoV-2 infection of cancer patients. Across some heterogeneity in tumor type, stage, and treatment, virus-exposed solid cancer patients display a dominant impact of SARS-CoV-2, apparent from the resemblance of their immune signatures to those for COVID-19+ non-cancer patients. This is not the case for hematological malignancies, with virus-exposed patients collectively displaying heterogeneous humoral responses, an exhausted T cell phenotype and a high prevalence of prolonged virus shedding. Furthermore, while recovered solid cancer patients' immunophenotypes resemble those of non-virus-exposed cancer patients, recovered hematological cancer patients display distinct, lingering immunological legacies. Thus, while solid cancer patients, including those with advanced disease, seem no more at risk of SARS-CoV-2-associated immune dysregulation than the general population, hematological cancer patients show complex immunological consequences of SARS-CoV-2 exposure that might usefully inform their care.

Methods for Modification of Therapeutic Viruses.

The optimal clinical exploitation of viruses as gene therapy or oncolytic vectors will require them to be administered intravenously. Strategies must therefore be deployed to enable viruses to survive the harsh neutralizing environment of the bloodstream and achieve deposition within and throughout target tissues or tumor deposits. This chapter describes the genetic and chemical engineering approaches that are being developed to overcome these challenges.

Magnetic microbubble mediated chemo-sonodynamic therapy using a combined magnetic-acoustic device.

Recent pre-clinical studies have demonstrated the potential of combining chemotherapy and sonodynamic therapy for the treatment of pancreatic cancer. Oxygen-loaded magnetic microbubbles have been explored as a targeted delivery vehicle for this application. Despite preliminary positive results, a previous study identified a significant practical challenge regarding the co-alignment of the magnetic and ultrasound fields. The aim of this study was to determine whether this challenge could be addressed through the use of a magnetic-acoustic device (MAD) combining a magnetic array and ultrasound transducer in a single unit, to simultaneously concentrate and activate the microbubbles at the target site. in vitro experiments were performed in tissue phantoms and followed by in vivo treatment of xenograft pancreatic cancer (BxPC-3) tumours in a murine model. In vitro, a 1.4-fold (p < .01) increase in the deposition of a model therapeutic payload within the phantom was achieved using the MAD compared to separate magnetic and ultrasound devices. In vivo, tumours treated with the MAD had a 9% smaller mean volume 8 days after treatment, while tumours treated with separate devices or microbubbles alone were respectively 45% and 112% larger. This substantial and sustained decrease in tumour volume suggests that the proposed drug delivery approach has the potential to be an effective neoadjuvant therapy for pancreatic cancer patients.

The cellular uptake of meta-tetra(hydroxyphenyl)chlorin entrapped in organically modified silica nanoparticles is mediated by serum proteins.

Nanosized objects made of various materials are gaining increasing attention as promising vehicles for the delivery of therapeutic and diagnostic agents for cancer. Photodynamic therapy (PDT) appears to offer a very attractive opportunity to implement drug delivery systems since no release of the sensitizer is needed to obtain the therapeutic effect and the design of the nanovehicle should be much easier. The aim of our study was to investigate the use of organic-modified silica nanoparticles (NPs) for the delivery of the second-generation photosensitizer meta-tetra(hydroxyphenyl)chlorin (mTHPC) to cancer cells in vitro. mTHPC was entrapped in NPs (approximately 33 nm diameter) in a monomeric form which produced singlet oxygen with a high efficiency. In aqueous media with high salt concentrations, the NPs underwent aggregation and precipitation but their stability could be preserved in the presence of foetal bovine serum. The cellular uptake, localization and phototoxic activity of mTHPC was determined comparatively in human oesophageal cancer cells after its delivery by the NPs and the standard solvent ethanol/poly(ethylene glycol) 400/water (20:30:50, by vol). The NP formulation reduced the cellular uptake of mTHPC by about 50% in comparison to standard solvent while it did not affect the concentration-dependent photokilling activity of mTHPC and its intracellular localization. Fluorescence resonance energy transfer measurements, using NPs with mTHPC physically entrapped and a cyanine covalently linked, and ultracentrifugation experiments indicated that mTHPC is transferred from NPs to serum proteins when present in the medium. However, the coating of the NP surface with poly(ethylene glycol) largely prevented the transfer to proteins. In conclusion, mTHPC is rapidly transferred from the uncoated nanoparticles to the serum proteins and then internalized by the cells as a protein complex, irrespective of its modality of delivery.

Comparing Strategies for Magnetic Functionalization of Microbubbles.

The advancement of ultrasound-mediated therapy has stimulated the development of drug-loaded microbubble agents that can be targeted to a region of interest through an applied magnetic field prior to ultrasound activation. However, the need to incorporate therapeutic molecules while optimizing the responsiveness to both magnetic and acoustic fields and maintaining adequate stability poses a considerable challenge for microbubble synthesis. The aim of this study was to evaluate three different methods for incorporating iron oxide nanoparticles (IONPs) into phospholipid-coated microbubbles using (1) hydrophobic IONPs within an oil layer below the microbubble shell, (2) phospholipid-stabilized IONPs within the shell, or (3) hydrophilic IONPs noncovalently bound to the surface of the microbubble. All microbubbles exhibited similar acoustic response at both 1 and 7 MHz. The half-life of the microbubbles was more than doubled by the addition of IONPs by using both surface and phospholipid-mediated loading methods, provided the lipid used to coat the IONPs was the same as that constituting the microbubble shell. The highest loading of IONPs per microbubble was also achieved with the surface loading method, and these microbubbles were the most responsive to an applied magnetic field, showing a 3-fold increase in the number of retained microbubbles compared to other groups. For the purpose of drug delivery, surface loading of IONPs could restrict the attachment of hydrophilic drugs to the microbubble shell, but hydrophobic drugs could still be incorporated. In contrast, although the incorporation of phospholipid IONPs produced more weakly magnetic microbubbles, it would not interfere with hydrophilic drug loading on the surface of the microbubble.

Microbubbles, Nanodroplets and Gas-Stabilizing Solid Particles for Ultrasound-Mediated Extravasation of Unencapsulated Drugs: An Exposure Parameter Optimization Study.

Ultrasound-induced cavitation has been proposed as a strategy to tackle the challenge of inadequate extravasation, penetration and distribution of therapeutics into tumours. Here, the ability of microbubbles, droplets and solid gas-trapping particles to facilitate mass transport and extravasation of a model therapeutic agent following ultrasound-induced cavitation is investigated. Significant extravasation and penetration depths on the order of millimetres are achieved with all three agents, including the range of pressures and frequencies achievable with existing clinical ultrasound systems. Deeper but highly directional extravasation was achieved with frequencies of 1.6 and 3.3 MHz compared with 0.5 MHz. Increased extravasation was observed with increasing pulse length and exposure time, while an inverse relationship is observed with pulse repetition frequency. No significant cell death or any haemolytic activity in human blood was observed at clinically relevant concentrations for any of the agents. Overall, solid gas-trapping nanoparticles were found to enable the most extensive extravasation for the lowest input acoustic energy, followed by microbubbles and then droplets. The ability of these agents to produce sustained inertial cavitation activity whilst being small enough to follow the drug out of the circulation and into diseased tissue, combined with a good safety profile and the possibility of real-time monitoring, offers considerable potential for enhanced drug delivery of unmodified drugs in oncological and other biomedical applications.

Gas-Stabilizing Gold Nanocones for Acoustically Mediated Drug Delivery.

The efficient penetration of drugs into tumors is a major challenge that remains unmet. Reported herein is a strategy to promote extravasation and enhanced penetration using inertial cavitation initiated by focused ultrasound and cone-shaped gold nanoparticles that entrap gas nanobubbles. The cones are capable of initiating inertial cavitation under pressures and frequencies achievable with existing clinical ultrasound systems and of promoting extravasation and delivery of a model large therapeutic molecule in an in vitro tissue mimicking flow phantom, achieving penetration depths in excess of 2 mm. Ease of functionalization and intrinsic imaging capabilities provide gold with significant advantages as a material for biomedical applications. The cones show neither cytotoxicity in Michigan Cancer Foundation (MCF)-7 cells nor hemolytic activity in human blood at clinically relevant concentrations and are found to be colloidally stable for at least 5 d at 37 °C and several months at 4 °C.

Optimization of molecularly targeted MRI in the brain: empirical comparison of sequences and particles.

BACKGROUND: Molecular MRI is an evolving field of research with strong translational potential. Selection of the appropriate MRI sequence, field strength and contrast agent depend largely on the application. The primary aims of the current study were to: 1) assess the sensitivity of different MRI sequences for detection of iron oxide particles in mouse brain; 2) determine the effect of magnetic field strength on detection of iron oxide particles in vivo; and 3) compare the sensitivity of targeted microparticles of iron oxide (MPIO) or ultra-small superparamagnetic iron oxide (USPIO) for detection of vascular cell adhesion molecule-1 (VCAM-1) in vivo. METHODS: Mice were injected intrastriatally with interleukin 1ß to induce VCAM-1 expression on the cerebral vasculature. Subsequently, animals were injected intravenously with either VCAM-MPIO or VCAM-USPIO and imaged 1 or 13 hours post-injection, respectively. MRI was performed at 4.7, 7.0, or 9.4 T, using three different T2*-weighted sequences: single gradient echo 3D (GE3D), multi-gradient echo 3D (MGE3D) and balanced steady-state free precession 3D (bSSFP3D). RESULTS: MGE3D yielded the highest signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for the detection of iron oxide particles. All sequences showed a significant increase in SNR and CNR from 4.7 to 7.0 T, but no further improvement at 9.4 T. However, whilst targeted MPIO enabled sensitive detection of VCAM-1 expression on the cerebral vasculature, the long half-life (16.5 h vs 1.2 min) and lower relaxivity per particle (1.29×10-14 vs 1.18×10-9 Hz L/particle) of USPIO vs. MPIO rendered them impractical for molecular MRI. CONCLUSION: These findings demonstrate clear advantages of MPIO compared to USPIO for molecularly-targeted MRI, and indicate that the MGE3D sequence is optimal for MPIO detection. Moreover, higher field strengths (7.0/9.4 T) showed enhanced sensitivity over lower field strengths (4.7 T). With the development of biodegradable MPIO, these agents hold promise for clinical translation.

Ultrasound-mediated cavitation does not decrease the activity of small molecule, antibody or viral-based medicines.

The treatment of cancer using nanomedicines is limited by the poor penetration of these potentially powerful agents into and throughout solid tumors. Externally controlled mechanical stimuli, such as the generation of cavitation-induced microstreaming using ultrasound (US), can provide a means of improving nanomedicine delivery. Notably, it has been demonstrated that by focusing, monitoring and controlling the US exposure, delivery can be achieved without damage to surrounding tissue or vasculature. However, there is a risk that such stimuli may disrupt the structure and thereby diminish the activity of the delivered drugs, especially complex antibody and viral-based nanomedicines. In this study, we characterize the impact of cavitation on four different agents, doxorubicin (Dox), cetuximab, adenovirus (Ad) and vaccinia virus (VV), representing a scale of sophistication from a simple small-molecule drug to complex biological agents. To achieve tight regulation of the level and duration of cavitation exposure, a "cavitation test rig" was designed and built. The activity of each agent was assessed with and without exposure to a defined cavitation regime which has previously been shown to provide effective and safe delivery of agents to tumors in preclinical studies. The fluorescence profile of Dox remained unchanged after exposure to cavitation, and the efficacy of this drug in killing a cancer cell line remained the same. Similarly, the ability of cetuximab to bind its epidermal growth factor receptor target was not diminished following exposure to cavitation. The encoding of the reporter gene luciferase within the Ad and VV constructs tested here allowed the infectivity of these viruses to be easily quantified. Exposure to cavitation did not impact on the activity of either virus. These data provide compelling evidence that the US parameters used to safely and successfully delivery nanomedicines to tumors in preclinical models do not detrimentally impact on the structure or activity of these nanomedicines.

Electroformation of Giant Unilamellar Vesicles on Stainless Steel Electrodes.

Giant unilamellar vesicles (GUVs) are well-established model systems for studying membrane structure and dynamics. Electroformation, also referred to as electroswelling, is one of the most prevalent methods for producing GUVs, as it enables modulation of the lipid hydration process to form relatively monodisperse, defect-free vesicles. Currently, however, it is expensive and time-consuming compared with other methods. In this study, we demonstrate that 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine GUVs can be prepared readily at a fraction of the cost on stainless steel electrodes, such as commercially available syringe needles, without any evidence of lipid oxidation or hydrolysis.

Targeted delivery of photosensitizers: efficacy and selectivity issues revealed by multifunctional ORMOSIL nanovectors in cellular systems.

PEGylated and non-PEGylated ORMOSIL nanoparticles prepared by microemulsion condensation of vinyltriethoxy-silane (VTES) were investigated in detail for their micro-structure and ability to deliver photoactive agents. With respect to pure silica nanoparticles, organic modification substantially changes the microstructure and the surface properties. This in turn leads to a modulation of both the photophysical properties of embedded photosensitizers and the interaction of the nanoparticles with biological entities such as serum proteins. The flexibility of the synthetic procedure allows the rapid preparation and screening of multifunctional nanosystems for photodynamic therapy (PDT). Selective targeting of model cancer cells was tested by using folate, an integrin specific RGD peptide and anti-EGFR antibodies. Data suggest the interference of the stealth-conferring layer (PEG) with small targeting agents, but not with bulky antibodies. Moreover, we showed that selective photokilling of tumour cells may be limited even in the case of efficient targeting because of intrinsic transport limitations of active cellular uptake mechanisms or suboptimum localization.

A cell-penetrating ratiometric nanoprobe for intracellular chloride.

NanoChlor, a nanoparticle-based fluorescent probe for chloride that is both ratiometric and capable of spontaneously penetrating neuronal cells at submillimolar concentrations, was designed and studied. NanoChlor is built on silica nanoparticles grafted with 6-methoxyquinolinium as the chloride-sensitive component and fluorescein as the reference dye. A Stern-Volmer constant of 50 M(-1) was measured in Ringer's buffer at pH 7.2, and the response to chemically induced chloride currents was recorded in real time in hippocampal cells.

Sensing with fluorescent nanoparticles.

Fluorescent chemosensors are chemical systems that can detect and signal the presence of selected analytes through variations in their fluorescence emission. Their peculiar properties make them arguably one of the most useful tools that chemistry has provided to biomedical research, enabling the intracellular monitoring of many different species for medical and biological purposes. In its simplest design, a fluorescent chemosensor is composed of a fluorescent dye and a receptor, with a built-in transduction mechanism that converts recognition events into variations of the emission properties of the fluorescent dye. As soon as fluorescent nanoparticles became available, several applications in the field of sensing were explored. Nanoparticles have been used not only as better-performing substitutes of traditional dyes but also as multivalent scaffolds for the realization of supramolecular assemblies, while their high surface to volume ratio allows for distinct spatial domains (bulk, external surface, pores and shells) to be functionalized to a comparable extent with different organic species. Over the last few years, nanoparticles proved to be versatile synthetic platforms for the implementation of new sensing schemes.