Emergence of Non-Hexagonal Crystal Packing of Deswollen and Deformed Ultra-Soft Microgels under Osmotic Pressure Control.

Highly solvent swollen poly(N-isopropylacrylamide-co-acrylic acid) microgels are synthesized without exogenous crosslinker, making them extremely soft and deformable. These ultralow crosslinked microgels (ULC) are incubated under controlled osmotic pressure to provide a slow (and presumably thermodynamically controlled) approach to higher packing densities. It is found that ULC microgels show stable colloidal packing over a very wide range of osmotic pressures and thus packing densities.

Deswelling Induced Morphological Changes in Dual pH and Temperature Responsive Ultra-Low Crosslinked Poly (-isopropyl acrylamide)--Acrylic Acid Microgels.

Poly(-isopropylacrylamide) microgels prepared without exogenous crosslinker are extremely "soft" as a result of their very low crosslinking density, with network connectivity arising only from the self-crosslinking of pNIPAm chains. As a result of this extreme softness, our group and others have taken interest in using these materials in a variety of bioengineering applications, while also pursuing studies of their fundamental properties. Here, we report deswelling triggered structural changes in poly (-isopropylacrylamide--acrylic acid) (ULC10AAc) microgels prepared by precipitation polymerization.

Poly (N-Isopropylacrylamide) microgel-based optical devices for humidity sensing.

Optical sensors for environmental humidity have been constructed from poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels. The devices were constructed by first depositing a monolithic layer of pNIPAm-co-AAc microgels on a Au-coated glass substrate followed by the addition of another Au layer on top. The resultant assembly showed visual color, and exhibited multipeak reflectance spectra.

Photothermally Induced Optical Property Changes of Poly(N-isopropylacrylamide) Microgel-Based Etalons.

Poly(N-isopropylacrylamide) microgel-based optical devices were designed such that they can be stimulated to change their optical properties in response to light produced by a light-emitting diode (LED). The devices were fabricated by sandwiching the synthesized microgels between two Cr/Au layers all supported on a glass coverslip with gold nanoparticles (AuNPs) deposited. Here, we found that these devices can be stimulated to change their optical properties when exposed to green LED light, which excites the AuNPs and increases the local temperature, causing the thermoresponsive microgels to decrease in diameter, resulting in a change in the devices' optical properties.

A novel label-free colorimetric assay for DNA concentration in solution.

Optical devices were fabricated by sandwiching a "monolithic" poly(N-isopropylacrylamide-co-N-(3-aminopropyl) methacrylamide hydrochloride) (pNIPAm-co-APMAH) microgel layer between two semitransparent Au layers. These devices, referred to as etalons, exhibit characteristic multipeak reflectance spectra, and the position of the peaks in the spectra primarily depends on the distance between the Au surfaces mediated by the microgel layer thickness. Here, we show that the positively charged microgel layer can collapse in the presence of negatively charged single stranded DNA (ssDNA) due to ssDNA induced microgel crosslinking.

Poly (N-isopropylacrylamide) microgel-based optical devices for sensing and biosensing.

Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group's efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications.

Polymer-based devices for the label-free detection of DNA in solution: low DNA concentrations yield large signals.

Poly (N-isopropylacrylamide-co-N-(3-aminopropyl) methacrylamide hydrochloride) microgel-based optical devices (etalons) have been shown to change their optical properties in the presence of single-stranded DNA. We hypothesize that this is due to the negatively charged DNA penetrating through the Au overlayer of the etalon, resulting in cross-linking and collapse of the positively charged microgels. We have shown that this technology is capable of detecting micromolar concentrations of target DNA in solutions containing two and four base pair mismatch sequences without the use of labels.

Responsive polymers for biosensing and protein delivery.

In this feature article, we review some recent advances in the field of materials chemistry for biosensing, and protein/drug delivery. Our recent work on the development of responsive polymer-based platforms for biosensing and drug delivery will also be highlighted. This feature article is meant to outline the breadth of the utility of polymer-based materials for select applications, as well as their enormous potential impact on future technologies.

Self-assembly of a set of hydrophilic-solvophobic-hydrophobic coil-rod-coil molecules based on perylene diimide.

The self-assembly and the resulting morphology of a set of asymmetrically substituted perylene diimide is discussed. We synthesized perylene diimides with hydrophilic Jeffamine® (PEO/PPO co-oligomer) attached to the imide nitrogen on one side and (hydrophobic) alkyl chains of different lengths on the other. Although studies on asymmetrically substituted perylene diimides have been reported by various authors, both side chains in this work are linear and we discuss the effect of the length of the hydrophobic alkyl side chain on the self-assembly in water and aqueous mixtures and the resulting morphology.

Unexpected cononsolvency behavior of poly (N-isopropylacrylamide)-based microgels.

Poly (N-isopropylacrylamide) (pNIPAm)-based microgels undergo a transition from fully water swollen (solvated) to deswollen (desolvated) as the temperature of the water they are dissolved in is increased >32 °C. In this submission, we examine how the temperature of this transition, i.e.

Microgel-based etalon coated quartz crystal microbalances for detecting solution pH: The effect of Au overlayer thickness.

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels were "painted" on the Au electrode of a quartz crystal microbalance (QCM). Another Au layer (overlayer) was subsequently deposited on the microgel layer. This structure is known as a microgel-based etalon.

Responsive polymers for analytical applications: a review.

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations.

Label-free detection of low protein concentration in solution using a novel colorimetric assay.

Dual pH and temperature sensitive microgel-based etalons were fabricated by sandwiching a "monolithic" microgel layer between two semitransparent, Au layers. The devices exhibit visual color and multipeak reflectance spectra, both of which primarily depend on the distance between the Au surfaces mediated by the microgel diameter. We found that a polycationic polyelectrolyte can penetrate through the Au overlayer to interact with negatively charged microgel confined between Au overlayers.

Polyelectrolyte mediated intra and intermolecular crosslinking in microgel-based etalons for sensing protein concentration in solution.

Biotin modified polycationic polymers are capable of penetrating the Au overlayer of poly(N-isopropylacrylamide)-co-acrylic acid microgel-based etalons. Once penetrated, the polycations crosslink the polyanionic microgels, causing them to collapse, resulting in a concomitant blue shift of the spectral peaks in the reflectance spectrum. We show that the magnitude of the blue shift depends on the concentration of the biotinylated polycation solution exposed to the etalon.

Tubular or subsurface morphology of octabutoxyphthalocyanine upon self-assembly in polymer matrices: effect of the casting solvent.

Spontaneous phase-separated, controlled aggregate structures of photo- and electroactive molecules in polymer matrices are of interest for device fabrication. We show that the self-assembly of octabutoxyphthalocyanine (Pc) in polymer matrices leads to tubular morphology of Pc when the film is prepared with tetrachloroethane (TCE) and subsurface droplet morphology with chloroform. The same morphology is seen with both bisphenol A polycarbonate (BPAPC) and poly(methyl methacrylate) (PMMA) as the matrix.

Deterioration of water quality of Surma river.

Surma River is polluted day by day by human activities, poor structured sewerage and drainage system, discharging industrial and household wastes. The charas (natural channels) are responsible for surface runoff conveyance from its urban catchments to the receiving Surma River. Water samples have been collected from a part of Surma River along different points and analyzed for various water quality parameters during dry and monsoon periods.