Smart hydrogel particles: biomarker harvesting: one-step affinity purification, size exclusion, and protection against degradation.

Disease-associated blood biomarkers exist in exceedingly low concentrations within complex mixtures of high-abundance proteins such as albumin. We have introduced an affinity bait molecule into N-isopropylacrylamide to produce a particle that will perform three independent functions within minutes, in one step, in solution: (a) molecular size sieving, (b) affinity capture of all solution-phase target molecules, and (c) complete protection of harvested proteins from enzymatic degradation. The captured analytes can be readily electroeluted for analysis.

Nanoparticles: potential biomarker harvesters.

A previously untapped bank of information resides within the low molecular weight proteomic fraction of blood. Intensive efforts are underway to harness this information so that it can be used for early diagnosis of diseases such as cancer. The physicochemical malleability and high surface areas of nanoparticle surfaces make them ideal candidates for developing biomarker harvesting platforms. Given the variety of engineering strategies afforded through nanoparticle technologies, a significant goal is to tailor nanoparticle surfaces to selectively bind a subset of biomarkers, sequestering them for later study using high sensitivity proteomic tests. To date, applications of nanoparticles have largely focused on imaging systems and drug delivery vectors. As such, biomarker harvesting is an underutilized application of nanoparticle technology and is an area of nanotechnology research that will likely undergo substantial growth.

Dynamic microcompartmentation in synthetic cells.

An experimental model for cytoplasmic organization is presented. We demonstrate dynamic control over protein distribution within synthetic cells comprising a lipid bilayer membrane surrounding an aqueous polymer solution. This polymer solution generally exists as two immiscible aqueous phases. Protein partitioning between these phases leads to microcompartmentation, or heterogeneous protein distribution within the "cell" interior. This model cytoplasm can be reversibly converted to a single phase by slight changes in temperature or osmolarity, such that local protein concentrations can be manipulated within the vesicle interior.

Microlens formation in microgel/gold colloid composite materials via photothermal patterning.

We report on the nature of photothermally patterned regions inside self-assembled hydrogel nanoparticle materials containing coassembled colloidal Au. These composite materials are prepared from approximately 226-nm diameter particles composed of the environmentally responsive polymer, poly(N-isopropylacrylamide) (pNIPAm). Upon centrifugation to achieve a proper volume fraction, these close-packed assemblies display a sharp Bragg diffraction peak in the midvisible region of the spectrum and can be reversibly converted into a nondiffracting glassy material as the temperature is raised above the characteristic phase transition temperature of the polymer. The addition of 16-nm colloidal Au prior to centrifugation allows the homogeneous distribution of metal nanoparticles throughout the close-packed material. Localized heating is then possible upon excitation of the Au plasmon absorption with a frequency doubled Nd:YAG laser (lambda = 532 nm). Such localized heating events lead to patterned regions of ordered crystalline phases inside of bulk glassy phases. We illustrate that the nature of the locally patterned area results in the formation of a microlens due to density/refractive index gradient in the patterned crystalline region. The Gaussian power distribution of the incident beam is thought to be a contributing factor in the microlens formation. Microlens formation is shown by observing interference patterns similar to Newton's rings, which change over time as the region is formed. A true hallmark of the lens is also demonstrated by focusing an image through the patterned structure.

Photothermal patterning of microgel/gold nanoparticle composite colloidal crystals.

We present a new method for laser direct writing in self-assembled hydrogel microparticle colloidal crystals via photothermal excitation of co-assembled colloidal Au particles. Close-packed colloidal crystals are assembled from approximately 224 nm diameter, thermoresponsive, poly-N-isopropylacrylamide hydrogel microparticles (microgels); these crystals display sharp Bragg diffraction peaks in the mid-visible region of the spectrum due to the periodic dielectric function of the assembly. Raising the temperature of the crystal above the characteristic volume phase transition temperature of the microgel particles results in a reversible melting of the crystalline material due to the particle-based deswelling event. This transition can be used either to anneal defects from the crystalline material or to controllably and reversibly convert the assembly from the colored, crystalline state to a nondiffracting glassy material. Crystal-to-glass transitions are similarly accomplished via photothermal excitation when 16 nm diameter colloidal Au particles are co-assembled with the responsive microgels. Excitation of the colloidal Au plasmon absorption with a frequency doubled Nd:YAG laser (lambda = 532 nm) results in optically directed conversion of either glasses to crystals or crystals to glasses, depending on the initial state of the assembly and the illumination time. These results represent a fundamentally new method for the patterning of self-assembled photonic materials.