Mainul Hossain

Three-Dimensional Microtissue Assay for High-Throughput Cytotoxicity of Nanoparticles

Traditional in vitro nanotoxicity researches are conducted on cultured two-dimensional (2D) monolayer cells and thereby cannot reflect organism response to nanoparticle toxicities at tissue levels. This paper describes a new, high-throughput approach to test in vitro nanotoxicity in three-dimensional (3D) microtissue array, where microtissues are formed by seeding cells in nonsticky microwells, and cells are allowed to aggregate and grow into microtissues with defined size and shape. Nanoparticles attach and diffuse into microtissues gradually, causing radial cytotoxicity among cells, with more cells being killed on the outer layers of the microtissue than inside. Three classical toxicity assays [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT), glucose-6-phosphate dehydrogenase (G6DP), and calcein AM and ethidium homodimer (calcein AM/EthD-1)] have been adopted to verify the feasibility of the proposed approach. Results show that the nanotoxicities derived from this method are significantly lower than that from traditional 2D cultured monolayer cells (p < 0.05). Equipped with a microplate reader or a microscope, the nanotoxicity assay could be completed automatically without transferring the microtissue, ensuring the reliability of toxicity assay. The proposed approach provides a new strategy for high-throughput, simple, and accurate evaluation of nanoparticle toxicities by combining 3D microtissue array with a panel of classical toxicity assays.

X-ray enabled detection and eradication of circulating tumor cells with nanoparticles

The early detection and eradication of circulating tumor cells (CTCs) play an important role in cancer metastasis management. This paper describes a new nanoparticle-enabled technique for integrated enrichment, detection and killing of CTCs by using magnetic nanoparticles and bismuth nanoparticles, X-ray fluorescence spectrometry, and X-ray radiation. The nanoparticles are modified with tumor targeting agents and conjugated with tumor cells through folate receptors over-expressed on cancer cells. A permanent micro-magnet is used to collect CTCs suspended inside a flowing medium that contains phosphate buffered saline (PBS) or whole blood. The characteristic X-ray emissions from collected bismuth nanoparticles, upon excitation with collimated X-rays, are used to detect CTCs. Results show that the method is capable of selectively detecting CTCs at concentrations ranging from 100-100,000 cells/mL in the buffer solution, with a detection limit of ≈ 100 CTCs/mL. Moreover, the dose of primary X-rays can be enhanced to kill the localized CTCs by radiation induced DNA damage, with minimal invasiveness, thus making in vivo personalized CTC management possible.

Visible light mediated killing of multidrug-resistant bacteria using photoacids

Increasing acidity is a promising method for bacterial inactivation by inhibiting the synthesis of intracellular proteins at low pH. However, conventional ways of pH control are not reversible, which can cause continuous changes in cellular and biological behaviours and are harmful to the host. Utilizing a photoacid that can reversibly alter pH over two units, we demonstrated a strong bacterial inhibition assisted by visible light. The pH value of the solution reverts back to the original level immediately after the irradiation is stopped. If a photoacid is combined with colistin, the minimum inhibitory concentration (MIC) of colistin on multidrug-resistant (MDR) Pseudomonas aeruginosa can be improved ∼32 times (from 8 to 0.25 μg mL-1), which significantly decreases the toxicity of colistin in clinics. Evidenced by the extremely low toxicity of the photoacid, this strategy is promising in MDR bacteria killing.

Highly sensitive thermal detection of thrombin using aptamer-functionalized phase change nanoparticles

This paper describes a novel thermal biosensing technique for the highly sensitive and selective detection of thrombin using RNA aptamer-functionalized phase change nanoparticles as thermal probes. The presence of thrombin in solution leads to attachment of nanoparticles onto a substrate modified with the same aptamer by forming sandwiched complexes. The phase changes of nanoparticles from solid to liquid adsorb heat energy and generate sharp melting peaks during linear temperature scans, where the positions and areas of the melting peaks reflect the presence and the amount of thrombin, respectively. A detection sensitivity of 22 nM is achieved on flat aluminum surfaces, and the sensitivity can be enhanced by four times using silicon nanopillar substrates that have higher surface area. The thermal detection is immune to colored species in solution and has been used directly to detect thrombin in serum samples. By combining the high specificity of aptamers and the large surface area of silicon nanostructures, the thermal signals obtained during phase change of nanoparticles provide a highly sensitive, selective and low-cost method for thrombin detection.

Multiplexed biomarker detection using x-ray fluorescence of composition-encoded nanoparticles

Multiple DNA and protein biomarkers have been detected based on characteristic x-ray fluorescence of a panel of metal and alloy nanoparticles, which are modified with ligands of biomarkers to create a one-to-one correspondence and immobilized on ligand-modified substrates after forming complexes with target biomarkers in three-strand or sandwich configuration. By determining the presence and concentration of nanoparticles using x-ray fluorescence, the nature and amount of biomarkers can be detected with limits of 1 nM for DNA and 1 ng/ml for protein. By combining high penetrating ability of x-rays, this method allows quantitative imaging of multiple biomarkers.

On-chip radiation biodosimetry with three-dimensional microtissues

This paper reports an image-based, on-chip microtissue radiation biodosimeter that can simultaneously monitor radiation responses of multiple mammalian cell types. The microtissue chip is fabricated by molding molten agarose gel onto microfabricated patterns to form microwells, and seeding a variety of cell suspensions into different microwells inside the agarose gel. The camera of a mobile phone is used to collect images of an array of microtissues, and the color changes of microtissues upon X-ray irradiation allow accurate determination of cell death, which is related to radiation dose. The images can be transferred wirelessly, allowing the biodosimeter to be used for convenient and field deployable monitoring of radiation exposure.

Three-Dimensional Micro/Nanomaterials Generated by Fiber-Drawing Nanomanufacturing

Fiber drawing nanomanufacturing (FDN) is a new high-yield method to make three-dimensional (3D) ordered micro- and nanostructured materials. The main equipment used in the FDN process is a fiber draw tower, which is similar to those used in industry to make optical fibers for telecommunications. In FDN, glassy materials such as silicate glasses and polymers either in rod form or in tube form with appropriate filling materials can be drawn into fibrous building blocks (FBBs), which can be assembled into ordered 3D structures or ordered bundles of fibers for the next drawing. By repeating the same drawing process several times, the diameters of FBBs can be reduced from centimeters stepwise down to sub-micrometers, while preserving the ordered structures of FBBs. Depending on the properties of glassy materials, the filling materials of choice can be semiconductor materials, glasses, metallic wires, or organic materials. This chapter briefly summarizes several aspects of the FDN technique including material selection, draw process, size control, and assembly and also discusses various examples of FDN.

Visual detection of mercury vapor using plasmonic nanoparticle array

The fast and sensitive detections of chemicals adsorption onto solid substrates are of importance to many fields. Ordered arrays of gold nanoparticles with strong surface plasmon resonances allow directly visualized detection of molecular scale adsorptions of mercury vapor on solid substrates. The adsorbed species change local dielectric constants surrounding plasmonic nanoparticles, leading to shifts of plasmon resonance peaks into short wavelength direction because of interactions of chemicals with nanoparticles. The magnitude of peak shifts is proportional to the amount of adsorbed chemicals in certain range, and is sufficiently large so that color changes can be seen directly by naked eyes. The ordered nanoparticles can be made over a large area at high yield, allowing a quantitative, passive, and sensitive detection of molecular species.