Delivery of optical contrast agents using Triton-X100, part 1: reversible permeabilization of live cells for intracellular labeling

A Pioglitazone Nanoformulation Designed for Cancer-Associated Fibroblast Reprogramming and Cancer Treatment

The recent focus of cancer therapeutics research revolves around modulating the immunosuppressive tumor microenvironment (TME) to enhance efficacy. The tumor stroma, primarily composed of cancer-associated fibroblasts (CAFs), poses significant obstacles to therapeutic penetration, influencing resistance and tumor progression. Reprogramming CAFs into an inactivated state has emerged as a promising strategy, necessitating innovative approaches. This study pioneers the design of a nanoformulation using pioglitazone, a Food and Drug Administration-approved anti-diabetic drug, to reprogram CAFs in the breast cancer TME. Glutathione (GSH)-responsive dendritic mesoporous organosilica nanoparticles loaded with pioglitazone (DMON-P) are designed for the delivery of cargo to the GSH-rich cytosol of CAFs. DMON-P facilitates pioglitazone-mediated CAF reprogramming, enhancing the penetration of doxorubicin (Dox), a therapeutic drug. Treatment with DMON-P results in the downregulation of CAF biomarkers and inhibits tumor growth through the effective delivery of Dox. This innovative approach holds promise as an alternative strategy for enhancing therapeutic outcomes in CAF-abundant tumors, particularly in breast cancer.

Correlating the Properties of Antibiotics with the Energetics of Partitioning in Colloidal Self-Assemblies and the Effect on the Binding of a Released Drug with a Target Protein

The bioavailability of drugs and the monitoring of efficient dosage requires drug delivery through suitable vehicles. The partitioning characteristics of the drugs in the delivery vehicles is determined by their molecular features and structure. A quantitative understanding of the partitioning of drugs into delivery media and its subsequent release and binding to the target protein is essential to deriving guidelines for rational drug design. We have studied the partitioning of aminoglycosides and macrolide antibiotic drugs kanamycin, gentamicin, azithromycin, and erythromycin in cationic, nonionic, and the mixture of cationic and nonionic self-assemblies. The quantitative aspects of drug partitioning followed by the monitoring of its interaction with target model protein bovine serum albumin on subsequent release have been performed by using a combination of spectroscopy and high-sensitivity calorimetry. The mechanisms of partitioning have been analyzed on the basis of the values of standard molar enthalpy, entropy, the Gibbs free-energy change, and stoichiometry of interaction. The integrity of the binding sites and the effects of the components of the self-assemblies and the released drug on the serum albumin were analyzed by using differential scanning calorimetry and circular dichroism spectroscopy. The thermodynamic signatures of drug partitioning and subsequent binding to target protein have enabled an in-depth correlation of the structure-property-energetics relationships which are crucial for the broader objective of rational drug design.

A Comprehensive Review on Intracellular Delivery

Intracellular delivery is considered an indispensable process for various studies, ranging from medical applications (cell-based therapy) to fundamental (genome-editing) and industrial (biomanufacture) approaches. Conventional macroscale delivery systems critically suffer from such issues as low cell viability, cytotoxicity, and inconsistent material delivery, which have opened up an interest in the development of more efficient intracellular delivery systems. In line with the advances in microfluidics and nanotechnology, intracellular delivery based on micro- and nanoengineered platforms has progressed rapidly and held great promises owing to their unique features. These approaches have been advanced to introduce a smorgasbord of diverse cargoes into various cell types with the maximum efficiency and the highest precision. This review differentiates macro-, micro-, and nanoengineered approaches for intracellular delivery. The macroengineered delivery platforms are first summarized and then each method is categorized based on whether it employs a carrier- or membrane-disruption-mediated mechanism to load cargoes inside the cells. Second, particular emphasis is placed on the micro- and nanoengineered advances in the delivery of biomolecules inside the cells. Furthermore, the applications and challenges of the established and emerging delivery approaches are summarized. The topic is concluded by evaluating the future perspective of intracellular delivery toward the micro- and nanoengineered approaches.

A surfactant polymer wound dressing protects human keratinocytes from inducible necroptosis

Chronic wounds show necroptosis from which keratinocytes must be protected to enable appropriate wound re-epithelialization and closure. Poloxamers, a class of synthetic triblock copolymers, are known to be effective against plasma membrane damage (PMD). The purpose of this study is to evaluate the efficacy of a specific poloxamer, surfactant polymer dressing (SPD), which is currently used clinically as wound care dressing, against PMD in keratinocytes. Triton X-100 (TX100) at sub-lytic concentrations caused PMD as demonstrated by the efflux of calcein and by the influx of propidium iodide and FM1-43. TX100, an inducer of necroptosis, led to mitochondrial fragmentation, depletion of nuclear HMGB1, and activation of signaling complex associated with necroptosis (i.e., activation of RIP3 and phosphorylation of MLKL). All responses following exposure of human keratinocytes to TX100 were attenuated by pre- or co-treatment with SPD (100 mg/ml). The activation and translocation of phospho-MLKL to the plasma membrane, taken together with depletion of nuclear HMGB1, characterized the observed cell death as necroptosis. Thus, our findings show that TX100-induced plasma membrane damage and death by necroptosis were both attenuated by SPD, allowing keratinocyte survival. The significance of such protective effects of SPD on keratinocytes in wound re-epithelialization and closure warrant further studies.

Cell-Permeant Bioadaptors for Cytosolic Delivery of Native Antibodies: A "Mix-and-Go" Approach

Antibodies are powerful tools that may potentially find wide applications in live-cell bioimaging, disease diagnostics, and therapeutics. Their practical applications have however remained limited thus far, owing to their inability to cross the cell membrane. Existing approaches for cytosolic delivery of functional antibodies are available, but they are constantly plagued by the need for chemical/genetic modifications, low delivery efficiency, and severe endolysosomal trapping. Consequently, it is of paramount importance to develop new strategies capable of highly efficient cytosolic delivery of native antibodies with immediate bioavailability. Herein, we report a modification-free, convenient "mix-and-go" strategy for the cytosolic delivery of native antibodies to different live mammalian cells efficiently, with minimal endolysosomal trapping and immediate bioavailability. By simply mixing a cell-permeant bioadaptor (derived from protein A or TRIM21) with a commercially available off-the-shelf antibody, the resulting noncovalent complex could be immediately used for intracellular delivery of native antibodies needed in subsequent cytosolic target engagement. The versatility of this approach was successfully illustrated in a number of applications, including antibody-based, live-cell imaging of the endogenous protein glutathionylation to detect oxidative cell stress, antibody-based activation of endogenous caspase-3, and inhibition of endogenous PTP1B activity, and finally TRIM21-mediated endogenous protein degradation for potential targeted therapy. Our results thus indicate this newly developed, "mix-and-go" antibody delivery method should have broad applications in chemical biology and future drug discovery.

Blind Resolution of Lifetime Components in Individual Pixels of Fluorescence Lifetime Images Using the Phasor Approach

The phasor approach is used in fluorescence lifetime imaging microscopy for several purposes, notably to calculate the metabolic index of single cells and tissues. An important feature of the phasor approach is that it is a fit-free method allowing immediate and easy to interpret analysis of images. In a recent paper, we showed that three or four intensity fractions of exponential components can be resolved in each pixel of an image by the phasor approach using simple algebra, provided the component phasors are known. This method only makes use of the rule of linear combination of phasors rather than fits. Without prior knowledge of the components and their single exponential decay times, resolution of components and fractions is much more challenging. Blind decomposition has been carried out only for cuvette experiments wherein the statistics in terms of the number of photons collected is very good. In this paper, we show that using the phasor approach and measurements of the decay at phasor harmonics 2 and 3, available using modern electronics, we could resolve the decay in each pixel of an image in live cells or mice liver tissues with two or more exponential components without prior knowledge of the values of the components. In this paper, blind decomposition is achieved using a graphical method for two components and a minimization method for three components. This specific use of the phasor approach to resolve multicomponents in a pixel enables applications where multiplexing species with different lifetimes and potentially different spectra can provide a different type of super-resolved image content.

Triton X-100-Modified Adenosine Triphosphate-Responsive siRNA Delivery Agent for Antitumor Therapy

Modified polyethyleneimine (PEI) has been widely used as siRNA delivery agents. Here, a new Triton X-100-modified low-molecular-weight PEI siRNA delivery agent is developed together with the coupling of 4-carboxyphenylboronic acid (PBA) and dopamine grafted vitamin E (VEDA). Triton X-100, a nonionic detergent, greatly improves the cellular uptake of siRNA as well as the siRNA escape from endosome/lysosome because of its high transmembrane ability. In addition, the boronate bond between PBA and VEDA of the transfection agent can be triggered to release its entrapped siRNA because of the high level of adenosine triphosphate (ATP) in cancer cells. The transfection agent is successfully applied to deliver siRNAs targeting endogenous genes of epidermal growth factor receptor (EGFR) and kinesin-5 (Eg5) to cancer cells, showing good results on Eg5 and EGFR silencing ability and inhibition of cancer cell migration. Further in vivo study indicates that the Triton X-100-modified transfection agent is also efficient to deliver siRNA to cancer cells and shows significant tumor growth inhibition on mice tumor models. These results indicate that the Triton X-100-modified ATP-responsive transfection agent is a promising gene delivery vector for target gene silencing in vitro and in vivo.

Restriction Enzyme Analysis of Double-Stranded DNA on Pristine Single-Walled Carbon Nanotubes

Nanoprobes such as single-walled carbon nanotubes (SWCNTs) are capable of label-free detection that benefits from intrinsic and photostable near-infrared fluorescence. Despite the growing number of SWCNT-based applications, uncertainty surrounding the nature of double-stranded DNA (dsDNA) immobilization on pristine SWCNTs has limited their use as optical sensors for probing DNA-protein interactions. To address this limitation, we study enzyme activity on unmodified dsDNA strands immobilized on pristine SWCNTs. Restriction enzyme activity on various dsDNA sequences was used to verify the retention of the dsDNA's native conformation on the nanotube surface and to quantitatively compare the degree of dsDNA accessibility. We report a 2.8-fold enhancement in initial enzyme activity in the presence of surfactants. Förster resonance electron transfer (FRET) analysis attributes this enhancement to increased dsDNA displacement from the SWCNT surface. Furthermore, the accessibility of native dsDNA was found to vary with DNA configuration and the spacing between the restriction site and the nanotube surface, with a minimum spacing of four base pairs (bp) from the anchoring site needed to preserve enzyme activity. Molecular dynamics (MD) simulations verify that the anchored dsDNA remains within the vicinity of the SWCNT, revealing an unprecedented bimodal displacement of the bp nearest to SWCNT surface. Together, these findings illustrate the successful immobilization of native dsDNA on pristine SWCNTs, offering a new near-infrared platform for exploring vital DNA processes.

Vector-free intracellular delivery by reversible permeabilization

Despite advances in intracellular delivery technologies, efficient methods are still required that are vector-free, can address a wide range of cargo types and can be applied to cells that are difficult to transfect whilst maintaining cell viability. We have developed a novel vector-free method that uses reversible permeabilization to achieve rapid intracellular delivery of cargos with varying composition, properties and size. A permeabilizing delivery solution was developed that contains a low level of ethanol as the permeabilizing agent. Reversal of cell permeabilization is achieved by temporally and volumetrically controlling the contact of the target cells with this solution. Cells are seeded in conventional multi-well plates. Following removal of the supernatant, the cargo is mixed with the delivery solution and applied directly to the cells using an atomizer. After a short incubation period, permeabilization is halted by incubating the cells in a phosphate buffer saline solution that dilutes the ethanol and is non-toxic to the permeabilized cells. Normal culture medium is then added. The procedure lasts less than 5 min. With this method, proteins, mRNA, plasmid DNA and other molecules have been delivered to a variety of cell types, including primary cells, with low toxicity and cargo functionality has been confirmed in proof-of-principle studies. Co-delivery of different cargo types has also been demonstrated. Importantly, delivery occurs by diffusion directly into the cytoplasm in an endocytic-independent manner. Unlike some other vector-free methods, adherent cells are addressed in situ without the need for detachment from their substratum. The method has also been adapted to address suspension cells. This delivery method is gentle yet highly reproducible, compatible with high throughput and automated cell-based assays and has the potential to enable a broad range of research, drug discovery and clinical applications.

An innovative strategy to obtain extraordinary specificity in immunofluorescent labeling and optical super resolution imaging of microtubules

An innovative immunofluorescent labeling strategy for microtubules is presented, which can greatly reduce non-specific binding and improve the immunolabeling specificity.

Visualization and detection of live and apoptotic cells with fluorescent carbon nanoparticles

Apoptosis is a genetically encoded cell death program that involves different processes occurring on molecular and sub-cellular levels. Here we report on its new features—the increased accumulation of fluorescent carbon nanoparticles (CDots) in cells and their changed distribution within cell interior, which can witness on altered mechanisms of their translocation through the membrane. The comparative studies of living (intact) and apoptotic cells were provided with two cell lines (HeLa, Vero) using two types of fluorescent nanoparticles (“violet” and “blue” CDots). In all studied cases the images of living and apoptotic cells were different; the apoptotic cells incorporated larger number of CDots resulting in their much brighter images. These nanoparticles are distributed in cell cytoplasm, however, when the cells are fixed and treated with detergent, their nucleus is also labeled. Flow cytometry allows distinguishing the sub-populations of living and apoptotic cells in their cultures and suggests a very cheap and easy way to characterize them.

Dual orientation of the outer membrane lipoprotein P6 of nontypeable haemophilus influenzae

The majority of outer membrane (OM) lipoproteins in Gram-negative bacteria are tethered to the membrane via an attached lipid moiety and oriented facing in toward the periplasmic space; a few lipoproteins have been shown to be surface exposed. The outer membrane lipoprotein P6 from the Gram-negative pathogenic bacterium nontypeable Haemophilus influenzae (NTHi) is surface exposed and a leading vaccine candidate for prevention of NTHi infections. However, we recently found that P6 is not a transmembrane protein as previously thought (L. V. Michel, B. Kalmeta, M. McCreary, J. Snyder, P. Craig, M. E. Pichichero, Vaccine 29:1624-1627, 2011). Here we pursued studies to show that P6 has a dual orientation, existing infrequently as surface exposed and predominantly as internally oriented toward the periplasmic space. Flow cytometry using three monoclonal antibodies with specificity for P6 showed surface staining of whole NTHi cells. Confocal microscopy imaging confirmed that antibodies targeted surface-exposed P6 of intact NTHi cells and not internal P6 in membrane-compromised or dead cells. Western blots of two wild-type NTHi strains and a mutant NTHi strain that does not express P6 showed that P6 antibodies do not detect a promiscuous epitope on NTHi. Depletion of targets to nonlipidated P6 significantly decreased bactericidal activity of human serum. Protease digestion of surface-exposed P6 demonstrated that P6 is predominantly internally localized in a manner similar to its homologue Pal in Escherichia coli. We conclude that P6 of NTHi is likely inserted into the OM in two distinct orientations, with the predominant orientation facing in toward the periplasm.

A new technique for reversible permeabilization of live cells for intracellular delivery of quantum dots

A major challenge with the use of quantum dots (QDs) for cellular imaging and biomolecular delivery is the attainment of QDs freely dispersed inside the cells. Conventional methods such as endocytosis, lipids based delivery and electroporation are associated with delivery of QDs in vesicles and/or as aggregates that are not monodispersed. In this study, we demonstrate a new technique for reversible permeabilization of cells to enable the introduction of freely dispersed QDs within the cytoplasm. Our approach combines osmosis driven fluid transport into cells achieved by creating a hypotonic environment and reversible permeabilization using low concentrations of cell permeabilization agents like Saponin. Our results confirm that highly efficient endocytosis-free intracellular delivery of QDs can be accomplished using this method. The best results were obtained when the cells were treated with 50 μg ml⁻¹ Saponin in a hypotonic buffer at a 3:2 physiological buffer:DI water ratio for 5 min at 4 °C.

Rapid Stereomicroscopic Imaging of HER2 Overexpression in Ex Vivo Breast Tissue Using Topically Applied Silica-Based Gold Nanoshells

Tumor margin detection for patients undergoing breast conservation surgery primarily occurs postoperatively. Previously, we demonstrated that gold nanoshells rapidly enhance contrast of HER2 overexpression in ex vivo tissue sections. Our ultimate objective, however, is to discern HER2 overexpressing tissue from normal tissue in whole, nonsectioned, specimens to facilitate rapid diagnoses. Here, we use targeted nanoshells to quickly and effectively visualize HER2 receptor expression in intact ex vivo human breast tissue specimens. Punch biopsies of human breast tissue were analyzed after a brief 5-minute incubation with and without HER2-targeted silica-gold nanoshells using two-photon microscopy and stereomicroscopy. Labeling was subsequently verified using reflectance confocal microscopy, darkfield hyperspectral imaging, and immunohistochemistry to confirm levels of HER2 expression. Our results suggest that anti-HER2 nanoshells used in tandem with a near-infrared reflectance confocal microscope and a standard stereomicroscope may potentially be used to discern HER2-overexpressing cancerous tissue from normal tissue in near real time and offer a rapid supplement to current diagnostic techniques.

Advances in molecular imaging: targeted optical contrast agents for cancer diagnostics

Over the last three decades, our understanding of the molecular changes associated with cancer development and progression has advanced greatly. This has led to new cancer therapeutics targeted against specific molecular pathways; such therapies show great promise to reduce mortality, in part by enabling physicians to tailor therapy for patients based on a molecular profile of their tumor. Unfortunately, the tools for definitive cancer diagnosis - light microscopic examination of biopsied tissue stained with nonspecific dyes - remain focused on the analysis of tissue ex vivo. There is an important need for new clinical tools to support the molecular diagnosis of cancer. Optical molecular imaging is emerging as a technique to help meet this need. Targeted, optically active contrast agents can specifically label extra- and intracellular biomarkers of cancer. Optical images can be acquired in real time with high spatial resolution to image-specific molecular targets, while still providing morphologic context. This article reviews recent advances in optical molecular imaging, highlighting the advances in technology required to improve early cancer detection, guide selection of targeted therapy and rapidly evaluate therapeutic efficacy.

Presynaptic imaging of projection fibers by in vivo injection of dextran-conjugated calcium indicators

Dextran-conjugated calcium indicators are stably retained within neurons. As a result, they are well suited to measuring presynaptic calcium at physiological temperatures. In addition, dextran indicators can be used to label neurons and their presynaptic boutons in vivo. This has allowed measurements of calcium in the presynaptic boutons of projection fibers that cannot be stably loaded with other types of indicators. This protocol describes a technique for in vivo loading of the climbing fiber projection to the cerebellum with dextran-conjugated indicators for subsequent presynaptic calcium imaging in brain slices. This technique is applicable to studies of projection fibers in many species from which brain slices can be prepared. The dextran indicator is injected into the inferior olive using a stereotaxic device. After a period of 1-3 d, cerebellar slices are prepared and presynaptic calcium transients are measured at physiological temperature in labeled climbing fibers. The protocol also discusses important considerations for using dextran-conjugated indicators to measure presynaptic calcium.

Increased blastocyst formation of cloned porcine embryos produced with donor cells pre-treated with Xenopus egg extract and/or digitonin

Pre-treating donor cells before somatic cell nuclear transfer (SCNT, 'cloning') may improve the efficiency of the technology. The aim of this study was to evaluate the early development of cloned embryos produced with porcine fibroblasts pre-treated with a permeabilizing agent and extract from Xenopus laevis eggs. In Experiment 1, fetal fibroblasts were permeabilized by digitonin, incubated in egg extract and, after re-sealing of cell membranes, cultured for 3 or 5 days before use as donor cells in handmade cloning (HMC). Controls were produced by HMC with non-treated donor cells. The blastocyst rate for reconstructed embryos increased significantly when digitonin-permeabilized, extract-treated cells were used after 5 days of culture after re-sealing. In Experiment 2, fetal and adult fibroblasts were treated with digitonin alone before re-sealing the cell membranes, then cultured for 3 or 5 days and used as donor cells in HMC. Treatment with digitonin alone increased the blastocyst rate, but only when fetal, and not adult fibroblasts, were used as donor cells, and only after 3 days of culture. In conclusion, we find a time window for increased efficiency of porcine SCNT using donor cells after pre-treatment with permeabilization/re-sealing and Xenopus egg extract. Interestingly, we observe a similar increase in cloning efficiency by permeabilization/re-sealing of donor cells without extract treatment that seems to depend on choice of donor cell type. Thus, pre-treatment of donor cells using permeabilizing treatment followed by re-sealing and in vitro culture for few days could be a simple way to improve the efficiency of porcine cloning.

Massive endocytosis driven by lipidic forces originating in the outer plasmalemmal monolayer: a new approach to membrane recycling and lipid domains

The roles that lipids play in endocytosis are the subject of debate. Using electrical and imaging methods, we describe massive endocytosis (MEND) in baby hamster kidney (BHK) and HEK293 cells when the outer plasma membrane monolayer is perturbed by the nonionic detergents, Triton X-100 (TX100) and NP-40. Some alkane detergents, the amphipathic drugs, edelfosine and tamoxifen, and the phospholipase inhibitor, U73122, are also effective. Uptake of the membrane tracer, FM 4–64, into vesicles and loss of reversible FM 4–64 binding confirm that 40–75% of the cell surface is internalized. Ongoing MEND stops in 2–4 s when amphipaths are removed, and amphipaths are without effect from the cytoplasmic side. Thus, expansion of the outer monolayer is critical. As found for Ca-activated MEND, vesicles formed are <100 nm in diameter, membrane ruffles are lost, and β-cyclodextrin treatments are inhibitory. However, amphipath-activated MEND does not require Ca transients, adenosine triphosphate (ATP) hydrolysis, G protein cycling, dynamins, or actin cytoskeleton remodeling. With elevated cytoplasmic ATP (>5 mM), MEND can reverse completely and be repeated multiple times in BHK and HEK293 cells, but not cardiac myocytes. Reversal is blocked by N-ethylmaleimide and a nitric oxide donor, nitroprusside. Constitutively expressed Na/Ca exchangers internalize roughly in proportion to surface membrane, whereas Na/K pump activities decrease over-proportionally. Sodium dodecyl sulfate and dodecylglucoside do not cause MEND during their application, but MEND occurs rapidly when they are removed. As monitored capacitively, the binding of these detergents decreases with MEND, whereas TX100 binding does not decrease. In summary, nonionic detergents can fractionate the plasma membrane in vivo, and vesicles formed connect immediately to physiological membrane-trafficking mechanisms. We suggest that lateral and transbilayer inhomogeneities of the plasma membrane provide potential energies that, when unbridled by triggers, can drive endocytosis by lipidic forces.

Fabrication of two-layered channel system with embedded electrodes to measure resistance across epithelial and endothelial barriers

This manuscript describes a straightforward fabrication process for embedding Ag/AgCl electrodes within a two-layer poly(dimethylsiloxane) (PDMS) microfluidic chip where an upper and a lower channel are separated by a semiporous membrane. This system allows for the reliable real-time measurement of transendothelial and transepithelial electrical resistance (TEER), an accepted quantification of cell monolayer integrity, across cells cultured on membranes inside the microchannels using impedance spectroscopy. The technique eliminates the need for costly or specialized microelectrode fabrication, enabling commercially available wire electrodes to easily be incorporated into PDMS microsystems for measuring TEER under microfluidic environments. The capability of measuring impedance across a confluent cell monolayer is confirmed using (i) brain-derived endothelial cells (bEND.3), (ii) Madin Darby Canine Kidney Cells (MDCK-2), and mouse myoblast (C2C12) (all from ATCC, Manassas, VA). TEER values as a function of cell type and cell culture time were measured and both agree with previously published values from macroscale culture techniques. This system opens new opportunities for conveniently resolving both transendothelial and transepithelial electrical resistance to monitor cell function in real-time in microfluidic cell cultures.

Efficient mucosal delivery of optical contrast agents using imidazole-modified chitosan

The clinical applicability of antibodies and plasmonic nanosensors as topically applied, molecule-specific optical diagnostic agents for noninvasive early detection of cancer and precancer is severely limited by our inability to efficiently deliver macromolecules and nanoparticles through mucosal tissues. We have developed an imidazole-functionalized conjugate of the polysaccharide chitosan (chitosan-IAA) to enhance topical delivery of contrast agents, ranging from small molecules and antibodies to gold nanoparticles up to 44 nm in average diameter. Contrast agent uptake and localization in freshly resected mucosal tissues was monitored using confocal microscopy. Chitosan-IAA was found to reversibly enhance mucosal permeability in a rapid, reproducible manner, facilitating transepithelial delivery of optical contrast agents. Permeation enhancement occurred through an active process, resulting in the delivery of contrast agents via a paracellular or a combined paracellular/transcellular route depending on size. Coadministration of epidermal growth factor receptor-targeted antibodies with chitosan-IAA facilitated specific labeling and discrimination between paired normal and malignant human oral biopsies. Together, these data suggest that chitosan-IAA is a promising topical permeation enhancer for mucosal delivery of optical contrast agents.