Multifunctional quantum dot DNA hydrogels

Biotemplated nanomaterials offer versatile functionality for multimodal imaging, biosensing, and drug delivery. There remains an unmet need for traceable and biocompatible nanomaterials that can be synthesized in a precisely controllable manner. Here, we report self-assembled quantum dot DNA hydrogels that exhibit both size and spectral tunability. We successfully incorporate DNA-templated quantum dots with high quantum yield, long-term photostability, and low cytotoxicity into a hydrogel network in a single step. By leveraging DNA-guided interactions, we introduce multifunctionality for a variety of applications, including enzyme-responsive drug delivery and cell-specific targeting. We report that quantum dot DNA hydrogels can be used for delivery of doxorubicin, an anticancer drug, to increase potency 9-fold against cancer cells. This approach also demonstrated high biocompatibility, trackability, and in vivo therapeutic efficacy in mice bearing xenografted breast cancer tumors. This work paves the way for the development of new tunable biotemplated nanomaterials with multiple synergistic functionalities for biomedical applications.

The development of nanomaterials for imaging and drug delivery has been of great interest to the field. Here, the authors synthesized multifunctional enzyme-responsive hydrogels with self-assembling quantum dots for nucleic acid and drug delivery as well as having imaging capability.

Biexciton Resonances Reveal Exciton Localization in Stacked Perovskite Quantum Wells

Quasi-two-dimensional lead halide perovskites, MA_n-1Pb_nX_3n+1, are quantum confined materials with an ever-developing range of optoelectronic device applications. Like other semiconductors, the correlated motion of electrons and holes dominates the material's response to optical excitation influencing its electrical and optical properties such as charge formation and mobility. However, the effects of many-particle correlation have been relatively unexplored in perovskite because of the difficultly of probing these states directly. Here, we use double quantum coherence spectroscopy to explore the formation and localization of multiexciton states in these materials. Between the most confined domains, we demonstrate the presence of an interwell, two-exciton excited state. This demonstrates that the four-body Coulomb interaction electronically couples neighboring wells despite weak electron/hole hybridization in these materials. Additionally, in contrast with inorganic semiconductor quantum wells, we demonstrate a rapid decrease in the dephasing time as wells become thicker, indicating that exciton delocalization is not limited by structural inhomogeneity in low-dimensional perovskite.

Amplified Micromagnetic Field Gradients Enable High-Resolution Profiling of Rare Cell Subpopulations

Analyzing small collections of cells is challenging because of the need for extremely high levels of sensitivity. We recently reported a new approach, termed magnetic ranking cytometry (MagRC), to profile nanoparticle-labeled cells. Using antibody-functionalized magnetic nanoparticles, we label cells so that each cell's magnetization is proportional to its surface expression of a selected biomarker. Using a microfluidic device that sorts the cells into 100 different zones based on magnetic labeling levels, we generate profiles that report on the level and distribution of surface expression in small collections of cells. Here, we present a new set of studies investigating in depth parameters such as flow rate and magnetic nanoparticle size that affect device performance using both experiments and modeling. We present a model that further elucidates the mechanism of cell capture and use it to optimize device performance to efficiently capture rare cells. We show that this method has excellent specificity and can be used to characterize rare cells even in the presence of whole blood.

Electrochemical DNA-Based Immunoassay That Employs Steric Hindrance To Detect Small Molecules Directly in Whole Blood

The development of a universal sensing mechanism for the rapid and quantitative detection of small molecules directly in whole blood would drastically impact global health by enabling disease diagnostics, monitoring, and treatment at home. We have previously shown that hybridization between a free DNA strand and its complementary surface-bound strand can be sterically hindered when the former is bound to large antibodies. Here, we exploit this effect to design a competitive antibody-based electrochemical assay, called CeSHHA, that enables the quantitative detection of small molecules directly in complex matrices, such as whole blood or soil. We discuss the importance of this inexpensive assay for point-of-care diagnosis and for treatment monitoring applications.

Isolation of Phenotypically Distinct Cancer Cells Using Nanoparticle-Mediated Sorting

Isolating subpopulations of heterogeneous cancer cells is an important capability for the meaningful characterization of circulating tumor cells at different stages of tumor progression and during the epithelial-to-mesenchymal transition. Here, we present a microfluidic device that can separate phenotypically distinct subpopulations of cancer cells. Magnetic nanoparticles coated with antibodies against the epithelial cell adhesion molecule (EpCAM) are used to separate breast cancer cells in the microfluidic platform. Cells are sorted into different zones on the basis of the levels of EpCAM expression, which enables the detection of cells that are losing epithelial character and becoming more mesenchymal. The phenotypic properties of the isolated cells with low and high EpCAM are then assessed using matrix-coated surfaces for collagen uptake analysis, and an NAD(P)H assay that assesses metabolic activity. We show that low-EpCAM expressing cells have higher collagen uptake and higher folate-induced NAD(P)H responses compared to those of high-EpCAM expressing cells. In addition, we tested SKBR3 cancer cells undergoing chemically induced hypoxia. The induced cells have reduced expression of EpCAM, and we find that these cells have higher collagen uptake and NAD(P)H metabolism relative to noninduced cells. This work demonstrates that nanoparticle-mediated binning facilitates the isolation of functionally distinct cell subpopulations and allows surface marker expression to be associated with invasiveness, including collagen uptake and metabolic activity.

Steric Hindrance Assay for Secreted Factors in Stem Cell Culture

The ex vivo expansion of hematopoietic stem cells is significantly inhibited by secreted proteins that induce negative feedback loops. The ability to effectively monitor these factors is critical for their real-time regulation and control and, by extension, enhancing stem cell expansion. Here, we describe a novel monitoring strategy for the detection of soluble signaling factors in stem cell cultures using a DNA-based sensing mechanism on a chip-based nanostructured microelectrode platform. We combine DNA hybridization engineering with antibody-capturing chemistry in an amplified steric hindrance hybridization assay. This method enables the quantification of important secreted proteins, showcased by the detection of 10 pg·mL^-1 level concentrations of three proteins in stem cell culture samples. This approach is the first universal nonsandwich technique that permits pg·mL^-1 level quantification of small proteins in stem cell culture media without signal loss.

Power-free, digital and programmable dispensing of picoliter droplets using a Digit Chip

There is a growing need for power-free methods to manipulate small volumes of liquids and thereby enable use of diagnostic assays in resource-limited settings. Most existing self-powered devices provide analog manipulation of fluids using paper, capillary or pressure-driven pumps. These strategies are well-suited to manipulating larger micro- and milliliter-scale volumes at constant flow rates; however, they fail to enable the manipulation of nanoliter and picoliter volumes required in assays using droplets, capillary sampling (e.g. finger prick), or expensive reagents. Here we report a device, termed the Digit Chip, that provides programmable and power-free digital manipulation of sub-nanoliter volumes. The device consists of a user-friendly button interface and a series of chambers connected by capillary valves that serve as digitization elements. Via a button press, the user dispenses and actuates ultra-small, quantitatively-programmed volumes. The device geometry is optimized using design models and experiments and precisely dispenses volumes as low as 21 pL with 97% accuracy. The volume dispensed can be tuned in 10 discrete steps across one order-of-magnitude with 98% accuracy. As a proof-of-principle that nanoliter-scale reagents can be precisely actuated and combined on-chip, we deploy the device to construct a precise concentration gradient with 10 discrete concentrations. Additionally, we apply this device alongside an inexpensive smartphone-based fluorescence imaging platform to perform a titration of E. coli with ampicillin. We observe the onset of bacterial death at a concentration of 5 μg mL^-1, increasing to a maximum at 50 μg mL^-1. These results establish the utility of the Digit Chip for diagnostic applications in low-resource environments.

Advancing Ultrasensitive Molecular and Cellular Analysis Methods to Speed and Simplify the Diagnosis of Disease

Diagnosing disease at the molecular level rapidly and with a high level of sensitivity and specificity is a critical capability for modern medicine. Rapid detection of small numbers of biomarkers of early disease in complex, heterogeneous clinical specimens represents a Holy Grail that will have a significant impact on human health.

Tracking the dynamics of circulating tumour cell phenotypes using nanoparticle-mediated magnetic ranking

Profiling the heterogeneous phenotypes of rare circulating tumour cells (CTCs) in whole blood is critical to unravelling the complex and dynamic properties of these potential clinical markers. This task is challenging because these cells are present at parts per billion levels among normal blood cells. Here we report a new nanoparticle-enabled method for CTC characterization, called magnetic ranking cytometry, which profiles CTCs on the basis of their surface expression phenotype. We achieve this using a microfluidic chip that successfully processes whole blood samples. The approach classifies CTCs with single-cell resolution in accordance with their expression of phenotypic surface markers, which is read out using magnetic nanoparticles. We deploy this new technique to reveal the dynamic phenotypes of CTCs in unprocessed blood from mice as a function of tumour growth and aggressiveness. We also test magnetic ranking cytometry using blood samples collected from cancer patients.

What Are Clinically Relevant Levels of Cellular and Biomolecular Analytes?

The ultimate goal of developing sensors for biomolecular analytes is to offer new tools for the analysis of clinical specimens for biomarkers of disease. It is thus important to understand the types of samples that are routinely used in the clinic for specific indications, and what the typical levels of relevant analytes are in these specimens. This Sensor Issues article summarizes information concerning levels of target molecules and cells that are of interest for the development of new diagnostics for infectious disease and cancer. Having this information in hand helps better define the "needle-in-a-haystack" challenge associated with developing robust sensors with the needed levels of sensitivity and specificity.

Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths

The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large-scale energy-harvesting applications.

Mitochondria-penetrating peptides conjugated to desferrioxamine as chelators for mitochondrial labile iron

Desferrioxamine (DFO) is a bacterial siderophore with a high affinity for iron, but low cell penetration. As part of our ongoing project focused on DFO-conjugates, we synthesized, purified, characterized and studied new mtDFOs (DFO conjugated to the Mitochondria Penetrating Peptides TAT_49-57, 1A, SS02 and SS20) using a succinic linker. These new conjugates retained their strong iron binding ability and antioxidant capacity. They were relatively non toxic to A2780 cells (IC50 40–100 μM) and had good mitochondrial localization (Rr +0.45 –+0.68) as observed when labeled with carboxy-tetramethylrhodamine (TAMRA) In general, mtDFO caused only modest levels of mitochondrial DNA (mtDNA) damage. DFO-SS02 retained the antioxidant ability of the parent peptide, shown by the inhibition of mitochondrial superoxide formation. None of the compounds displayed cell cycle arrest or enhanced apoptosis. Taken together, these results indicate that mtDFO could be promising compounds for amelioration of the disease symptoms of iron overload in mitochondria.

High-Curvature Nanostructuring Enhances Probe Display for Biomolecular Detection

High-curvature electrodes facilitate rapid and sensitive detection of a broad class of molecular analytes. These sensors have reached detection limits not attained using bulk macroscale materials. It has been proposed that immobilized DNA probes are displayed at a high deflection angle on the sensor surface, which allows greater accessibility and more efficient hybridization. Here we report the first use of all-atom molecular dynamics simulations coupled with electrochemical experiments to explore the dynamics of single-stranded DNA immobilized on high-curvature versus flat surfaces. We find that high-curvature structures suppress DNA probe aggregation among adjacent probes. This results in conformations that are more freely accessed by target molecules. The effect observed is amplified in the presence of highly charged cations commonly used in electrochemical biosensing. The results of the simulations agree with experiments that measure the degree of hybridization in the presence of mono-, di-, and trivalent cations. On high-curvature structures, hybridization current density increases as positive charge increases, whereas on flat electrodes, the trivalent cations cause aggregation due to electrostatic overscreening, which leads to decreased current density and less sensitive detection.

New Technologies for Rapid Bacterial Identification and Antibiotic Resistance Profiling

Conventional approaches to bacterial identification and drug susceptibility testing typically rely on culture-based approaches that take 2 to 7 days to return results. The long turnaround times contribute to the spread of infectious disease, negative patient outcomes, and the misuse of antibiotics that can contribute to antibiotic resistance. To provide new solutions enabling faster bacterial analysis, a variety of approaches are under development that leverage single-cell analysis, microfluidic concentration and detection strategies, and ultrasensitive readout mechanisms. This review discusses recent advances in this area and the potential of new technologies to enable more effective management of infectious disease.

High-Density Nanosharp Microstructures Enable Efficient CO2 Electroreduction

Conversion of CO₂ to CO powered by renewable electricity not only reduces CO₂ pollution but also is a means to store renewable energy via chemical production of fuels from CO. However, the kinetics of this reaction are slow due its large energetic barrier. We have recently reported CO₂ reduction that is considerably enhanced via local electric field concentration at the tips of sharp gold nanostructures. The high local electric field enhances CO₂ concentration at the catalytic active sites, lowering the activation barrier. Here we engineer the nucleation and growth of next-generation Au nanostructures. The electroplating overpotential was manipulated to generate an appreciably increased density of honed nanoneedles. Using this approach, we report the first application of sequential electrodeposition to increase the density of sharp tips in CO₂ electroreduction. Selective regions of the primary nanoneedles are passivated using a thiol SAM (self-assembled monolayer), and then growth is concentrated atop the uncovered high-energy planes, providing new nucleation sites that ultimately lead to an increase in the density of the nanosharp structures. The two-step process leads to a new record in CO₂ to CO reduction, with a geometric current density of 38 mA/cm² at -0.4 V (vs reversible hydrogen electrode), and a 15-fold improvement over the best prior reports of electrochemical surface area (ECSA) normalized current density.

Peptide-Mediated Delivery of Chemical Probes and Therapeutics to Mitochondria

Mitochondria are organelles with critical roles in key processes within eukaryotic cells, and their dysfunction is linked with numerous diseases including neurodegenerative disorders and cancer. Pharmacological manipulation of mitochondrial function is therefore important both for basic science research and eventually, clinical medicine. However, in comparison to other organelles, mitochondria are difficult to access due to their hydrophobic and dense double membrane system as well as their negative membrane potential. To tackle the challenge of targeting these important subcellular compartments, significant effort has been put forward to develop mitochondria-targeted systems capable of transporting bioactive cargo into the mitochondrial interior. Systems now exist that utilize small molecule, peptide, liposome, and nanoparticle-based transport. The vectors available vary in size and structure and can facilitate transport of a variety of compounds for mitochondrial delivery. Notably, peptide-based delivery scaffolds offer attractive features such as ease of synthesis, tunability, biocompatibility, and high uptake both in cellulo and in vivo. Owing to their simple and modular synthesis, these peptides are highly adaptable for delivering chemically diverse cargo. Key design features of mitochondria-targeted peptides include cationic charge, which allows them to harness the negative membrane potential of mitochondria, and lipophilicity, which permits favorable interaction with hydrophobic membranes of mitochondria. These peptides have been covalently tethered to target therapeutic agents, including anticancer drugs, to enhance their drug properties, and to provide probes for mitochondrial biology. Interestingly, mitochondria-targeted DNA damaging agents demonstrate high potency and the ability to evade resistance mechanisms and off-target effects. Moreover, a combination of mitochondria-targeted DNA damaging agents was applied to an siRNA screen for the elucidation of poorly understood mitochondrial DNA repair and replication pathways. In this work, a variety of novel proteins were identified that are essential for the maintenance of mitochondrial nucleic acids. Mitochondria-targeted peptides have also been used to increase the therapeutic window of antibacterial drugs with significant mammalian toxicity. Given the evolutionary similarity of mitochondria and bacteria, peptides are effective transporters that can target both of these entities. These antimicrobial peptides are highly effective even in difficult to target intracellular bacteria which reside within host cells. This peptide-based approach to targeting mitochondria has provided a variety of insights into the "druggability" of mitochondria and new biological processes that could be future drug targets. Nevertheless, the mitochondrial-targeting field is quite nascent and many exciting applications of organelle-specific conjugates remain to be explored. In this Account, we highlight the development and optimization of the mitochondria-penetrating peptides that our laboratory has developed, the unique applications of mitochondria-targeted bioactive cargo, and offer a perspective on important directions for the field.

Circulating Tumor Cells (CTC) and Cell-Free DNA (cfDNA) Workshop 2016: Scientific Opportunities and Logistics for Cancer Clinical Trial Incorporation

Despite the identification of circulating tumor cells (CTCs) and cell-free DNA (cfDNA) as potential blood-based biomarkers capable of providing prognostic and predictive information in cancer, they have not been incorporated into routine clinical practice. This resistance is due in part to technological limitations hampering CTC and cfDNA analysis, as well as a limited understanding of precisely how to interpret emergent biomarkers across various disease stages and tumor types. In recognition of these challenges, a group of researchers and clinicians focused on blood-based biomarker development met at the Canadian Cancer Trials Group (CCTG) Spring Meeting in Toronto, Canada on 29 April 2016 for a workshop discussing novel CTC/cfDNA technologies, interpretation of data obtained from CTCs versus cfDNA, challenges regarding disease evolution and heterogeneity, and logistical considerations for incorporation of CTCs/cfDNA into clinical trials, and ultimately into routine clinical use. The objectives of this workshop included discussion of the current barriers to clinical implementation and recent progress made in the field, as well as fueling meaningful collaborations and partnerships between researchers and clinicians. We anticipate that the considerations highlighted at this workshop will lead to advances in both basic and translational research and will ultimately impact patient management strategies and patient outcomes.

Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration

Electrochemical reduction of carbon dioxide (CO₂) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO₂ surrounding typical CO₂ reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO₂ adsorption, but this comes at the cost of increased hydrogen (H₂) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO₂ close to the active CO₂ reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO₂ reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.

Mitochondria-Targeted Doxorubicin: A New Therapeutic Strategy against Doxorubicin-Resistant Osteosarcoma

Doxorubicin is one of the leading drugs for osteosarcoma standard chemotherapy. A total of 40% to 45% of high-grade osteosarcoma patients are unresponsive, or only partially responsive, to doxorubicin (Dox), due to the overexpression of the drug efflux transporter ABCB1/P-glycoprotein (Pgp). The aim of this work is to improve Dox-based regimens in resistant osteosarcomas. We used a chemically modified mitochondria-targeted Dox (mtDox) against Pgp-overexpressing osteosarcomas with increased resistance to Dox. Unlike Dox, mtDox accumulated at significant levels intracellularly, exerted cytotoxic activity, and induced necrotic and immunogenic cell death in Dox-resistant/Pgp-overexpressing cells, fully reproducing the activities exerted by anthracyclines in drug-sensitive tumors. mtDox reduced tumor growth and cell proliferation, increased apoptosis, primed tumor cells for recognition by the host immune system, and was less cardiotoxic than Dox in preclinical models of drug-resistant osteosarcoma. The increase in Dox resistance was paralleled by a progressive upregulation of mitochondrial metabolism. By widely modulating the expression of mitochondria-related genes, mtDox decreased mitochondrial biogenesis, the import of proteins and metabolites within mitochondria, mitochondrial metabolism, and the synthesis of ATP. These events were paralleled by increased reactive oxygen species production, mitochondrial depolarization, and mitochondria-dependent apoptosis in resistant osteosarcoma cells, where Dox was completely ineffective. We propose mtDox as a new effective agent with a safer toxicity profile compared with Dox that may be effective for the treatment of Dox-resistant/Pgp-positive osteosarcoma patients, who strongly need alternative and innovative treatment strategies. Mol Cancer Ther; 15(11); 2640-52. ©2016 AACR.