We report here a reversible microchannel surface capture system for stimuli-responsive grafted bioanalytical beads. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto polydimethylsiloxane (PDMS) surfaces by a UV-mediated graft polymerization from a photoinitiator that was preadsorbed in the channel wall. The surface grafting density and resulting switchable hydrophilic/hydrophobic properties were controlled by varying the photo-illumination times and/or the initiator concentration. At limiting PNIPAAm-graft densities, the surfaces demonstrated minimal contact angles of 35 degrees below the lower critical solution temperature (LCST) and maximal contact angles of 82 degrees above it. These contact angles could be varied depending on the graft density. The surface grafts are spatially limited to the photo-illuminated region to define where the trap is constructed. The surface traps capture PNIPAAm-grafted nanobeads uniformly above the LCST and facilitate their rapid release as the temperature is reversed to below the LCST. This dual surface trap and injectable chromatography system could be useful in many applications, such as affinity separations, immunoassays, and enzyme bioprocesses, by providing for the controlled capture and release of chromatography beads. 相似文献
A stimuli-responsive magnetic nanoparticle system for diagnostic target capture and concentration has been developed for microfluidic lab card settings. Telechelic poly(N-isopropylacrylamide) (PNIPAAm) polymer chains were synthesized with dodecyl tails at one end and a reactive carboxylate at the opposite end by the reversible addition fragmentation transfer technique. These PNIPAAm chains self-associate into nanoscale micelles that were used as dimensional confinements to synthesize the magnetic nanoparticles. The resulting superparamagnetic nanoparticles exhibit a gamma-Fe2O3 core ( approximately 5 nm) with a layer of carboxylate-terminated PNIPAAm chains as a corona on the surface. The carboxylate group was used to functionalize the magnetic nanoparticles with biotin and subsequently with streptavidin. The functionalized magnetic nanoparticles can be reversibly aggregated in solution as the temperature is cycled through the PNIPAAm lower critical solution temperature (LCST). While the magnetophoretic mobility of the individual nanoparticles below the LCST is negligible, the aggregates formed above the LCST are large enough to respond to an applied magnetic field. The magnetic nanoparticles can associate with biotinylated targets as individual particles, and then subsequent application of a combined temperature increase and magnetic field can be used to magnetically separate the aggregated particles onto the poly(ethylene glycol)-modified polydimethylsiloxane channel walls of a microfluidic device. When the magnetic field is turned off and the temperature is reversed, the captured aggregates redisperse into the channel flow stream for further downstream processing. The dual magnetic- and temperature-responsive nanoparticles can thus be used as soluble reagents to capture diagnostic targets at a controlled time point and channel position. They can then be isolated and released after the nanoparticles have captured target molecules, overcoming the problem of low magnetophoretic mobility of the individual particle while retaining the advantages of a high surface to volume ratio and faster diffusive properties during target capture. 相似文献
The interaction forces between poly(N-isopropylacrylamide) (PNIPAAm)-grafted surfaces and colloidal particles in an aqueous solution were investigated using an atomic force microscope. Measurements were conducted between smooth silicon wafers on which PNIPAAm was terminally grafted and silica particles hydrophobized with a silanating reagent in an aqueous electrolyte solution under controlled temperature. Below the lower critical solution temperature (LCST) of PNIPAAm, there were large repulsive forces between the surfaces, both on approach and separation of the surfaces. On the other hand, above LCST, attractive forces were observed both in approaching and in separating force curves. When surface hydrophobicity of the particles increased, the maximum attractive force tended to increase. The changes of hydration state of the grafted PNIPAAm chains depending on temperature are considered to greatly alter the interaction force properties. The role of the intermolecular interaction between the PNIPAAm chains and the hydrophobic particles in the interaction forces is discussed. 相似文献
A facile route to well-defined "smart" polymer-protein conjugates with tunable bioactivity is reported. Protein modification with a reversible addition-fragmentation chain transfer (RAFT) agent and subsequent room temperature polymerization in aqueous media led to conjugates of poly(N-isopropylacrylamide) and a model protein. Representing the first example of polymer-protein conjugation with RAFT agent immobilization via the "R-group" approach, high molecular weight and reductively stable conjugates were accessible without extensive purification or adverse effects on the protein structure. An increase in molecular weight with conversion was observed for the chains grafted from the protein surface, confirming the controlled nature of the polymerization. The responsive behavior of the immobilized polymer facilitated conjugate isolation and also allowed environmental modulation of bioactivity. 相似文献
There is a current need for simple methods for immobilizing biomolecules within microfluidic channels. Here, a technique is reported for reversibly immobilizing immunoassay components in a channel zone that can be simply controlled by integrated heating elements. Latex beads were modified with the temperature-responsive polymer poly(N-isopropylacrylamide)(PNIPAAm) and co-modified with biotinylated poly(ethylene glycol)(PEG). PNIPAAm undergoes a hydrophilic-to-hydrophobic transition when the temperature is raised above the lower critical solution temperature (LCST)( approximately 28 degrees C in the solutions used here). This reversible transition drives the aggregation and dis-aggregation of the modified beads in heated zones within poly(ethylene terephthalate)(PET) microchannels. Biotinylated monoclonal antibodies for the drug digoxin were bound via streptavidin to the biotin-PEG-coated beads. These antibody-functionalized beads were then reversibly immobilized by aggregation and hydrophobic adhesion to the surface of PET microfluidic channels in response to a thermal stimulus. The antibodies on the beads immobilized in the channel were shown to bind digoxin and a competitor fluorescent ligand from a flow stream in a quantitative competitive assay format that reported the digoxin concentration. The antibodies could be replenished for each immunoassay trial, using the reversible, temperature-controlled immobilization process. This technique allows reagent immobilization immediately prior to an analytical procedure, following the removal of previously utilized beads, guaranteeing fresh and active immobilized biomolecules. Furthermore, it provides a simple approach to multiplexing through the simultaneous or sequential injection of different antibody-coated bead species, potentially at multiple sites in the integrated device channels. 相似文献
In this study, temperature-responsive polymer-protein conjugate was synthesized using a “grafting from” concept by introducing a chain transfer agent (CTA) into bovine serum albumin (BSA). The BSA-CTA was used as a starting point for poly(N-isopropylacrylamide) (PNIPAAm) through reversible addition-fragmentation chain transfer polymerization. The research investigations suggest that the thermally responsive behavior of PNIPAAm was controlled by the monomer ratio to CTA, as well as the amount of CTA introduced to BSA. The study further synthesized the human serum albumin (HSA)-PNIPAAm conjugate, taking the advantage that HSA can specifically adsorb indoxyl sulfate (IS) as a uremic toxin. The HSA-PNIPAAm conjugate could capture IS and decreased the concentration by about 40% by thermal precipitation. It was also revealed that the protein activity was not impaired by the conjugation with PNIPAAm. The proposed strategy is promising in not only removal of uremic toxins but also enrichment of biomarkers for early diagnostic applications. 相似文献
Summary: A series of thermally responsive dendritic core-shell polymers were prepared based upon dendritic polyamidoamine (PAMAM), modified with carboxyl end-capped linear poly(N-isopropylacrylamide) (PNIPAAm-COOH) in different ratios via an esterification process to obtain PNIPAAm-g-PAMAM. The graft ratio of PNIPAAm could be adjusted by changing the feed ratio of PAMAM-OH to PNIPAAm-COOH and was verified by 1H NMR and gel penetration chromatography (GPC). The lower critical solution temperature (LCST) of PNIPAAm-g-PAMAM evaluated by UV-vis spectrophotometer was about 32 °C. Indomethacin (IMC) as a model drug was loaded in the thermosensitive polymer-grafted dendrimer derivative and its release behavior was studied below and above its LCST (27 °C vs 37 °C). Results showed that the LCST of PNIPAAm-g-PAMAM was around 32 °C compared with that of the pure PNIPAAm. The release behavior of the indomethacin entrapped in the internal cavities of the PNIPAAm-g-PAMAM showed that almost 77% of the drug was cumulatively released at 27 °C after 10 hours, whereas only 20% was released at 37 °C. The release rate of IMC from the IMC/PNIPAAm-g-PAMAM complex at 37 °C is significantly slower than that at 27 °C, which indicates that the PNIPAAm chains grafted on the surface of PAMAM dendrimer could act as a channel switching on-off button through expending or contracting in response to the temperature variation and could control the drug release by varying the surrounding temperature. 相似文献
We have grafted temperature-responsive tethered poly(N-isopropylacrylamide) (PNIPAAm) onto silicon surfaces through atom transfer radical polymerization (ATRP) as a medium to extract human genomic DNA molecules from a biological specimen, namely human blood incorporating target DNA (hgDNA584) and control DNA (hgDNA528) at concentrations of 0.5, 1, and 50 ng μL(-1). The variable adhesion forces of the tethered PNIPAAm brushes on the surfaces were used to capture and release DNA molecules through changes in temperature. After amplifying the signal of the hgDNA584 and hgDNA528 strands released from the tethered PNIPAAm on the substrate using the polymerase chain reaction (PCR), we identified these DNA macromolecules using agarose gel electrophoresis. The accuracy of the detection of hgDNA584 and hgDNA528 was controlled through the design of specific primers in the PCR process. The quantities of these two DNA molecules obtained through the capture and release from tethered PNIPAAm brushes under temperature tuning conditions were sufficient for them to be amplified recognizably, suggesting that this approach could be used in miniaturized lab-on-a-chip cartridges for rapid disease diagnosis. 相似文献
We report actively controlled transport that is thermally switchable and size-selective in a nanocapillary array membrane (NCAM) prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) brushes onto the exterior surface of a Au-coated polycarbonate track-etched membrane. A smooth Au layer on the membrane surface, which is key to obtaining a uniform polymer film, was prepared by thermal evaporation of approximately 50 nm Au on both exterior surfaces. After evaporation, the inner diameter of the pore is reduced slightly, but the NCAM retains a narrow pore size distribution. PNIPPAm brushes with 10-30 nm (dry film) thickness were grafted onto the Au surface through surface-initiated atom transfer radical polymerization (ATRP) using a disulfide initiator, (BrC(CH3)2COO(CH2)11S)2. Molecular transport through the PNIPAAm polymer brush-modified NCAMs was investigated by real-time fluorescence measurements using fluorescein isothiocyanate (FITC)-labeled dextrans ranging from 4.4 to 282 kDa in membranes with variable initial pore diameters (80, 100, and 200 nm) and different PNIPAAm thicknesses. Manipulating the temperature of the NCAM through the PNIPAAm lower critical solution temperature (LCST) causes large, size-dependent changes in the transport rates. Over specific ranges of probe size, transport is completely blocked below the LCST but strongly allowed above the LCST. The combination of the highly uniform PNIPAAm brush and the monodisperse pore size distribution is critical in producing highly reproducible switching behavior. Furthermore, the reversible nature of the switching raises the possibility of using them as actively controlled filtration devices. 相似文献
A new temperature‐responsive porous monolith has been prepared by surface‐initiated activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) grafting poly(N‐isopropylacrylamide) (PNIPAAm) within the pores of the porous polymer monolith. The grafting copolymerization was carried out by a method based on a continuous flow‐through technique without special deoxygenation procedure needed in the general ATRP. The addition of ascorbic acid could counteract the oxidation effect of oxygen diffusing into the reaction system. The resulting grafted monolith was characterized by a mercury intrusion method and the size of macropore was 3.65 µm, which was suitable for flow through the monolith for HPLC. The thermally responsive property of the grafted monolith was evaluated by HPLC using steroids with various hydrophobicities as probes. Through determination of retention factor of each steroid on the grafted monolith at different temperatures using water as mobile phase, it was found that the slope of the plot of retention factor of each steroid versus the temperature changed around the low critical solution temperature (LCST, 32°C) of PNIPAAm in water. It was relative to the grafted PNIPAAm temperature sensitivity that a hydrophobic and hydrophilic alternation would take place around its LCST. Based on this thermally responsive property, the grafted monolith was used as stationary phase for HPLC and to separate the steroids using water as mobile phase by changing the column temperature. As a mobile phase, water is much better than organic solvents concerning the environment. 相似文献
This article describes the fabrication and characterization of stimulus-responsive elastin-like polypeptide (ELP) nanostructures grafted onto omega-substituted thiolates that were patterned onto gold surfaces by dip-pen nanolithography (DPN). In response to external stimuli such as changes in temperature or ionic strength, ELPs undergo a switchable and reversible, hydrophilic-hydrophobic phase transition at a lower critical solution temperature (LCST). We exploited this phase transition behavior to reversibly immobilize a thioredoxin-ELP (Trx-ELP) fusion protein onto the ELP nanopattern above the LCST. Subsequent binding of an anti-thioredoxin monoclonal antibody (anti-Trx) to the surface-captured thioredoxin showed the presentation of the immobilized protein in a sterically accessible orientation in the nanoarray. We also showed that the resulting Trx-ELP/anti-Trx complex formed above the LCST could be reversibly dissociated below the LCST. These results demonstrate the intriguing potential of ELP nanostructures as generic, reversible, biomolecular switches for on-chip capture and release of a small number (order 100-200) of protein molecules in integrated, nanoscale bioanalytical devices. We also investigated the molecular mechanism underlying this switch by measuring the height changes that accompany the binding and desorption steps and by adhesion force spectroscopy using atomic force microscopy. 相似文献
Interpenetrating polymer networks (IPNs) based on poly (N-isopropylacrylamide), (PNIPAAm) and poly (N-acryloxysuccinimide) (PNAS), grafted onto polypropylene (PP), were synthesized in three consecutive steps using ionizing radiation in the first and second steps and chemical reaction in third one. In the first step a thermosensitive graft copolymer of NIPAAm onto PP film was obtained by gamma radiation with a 60Co source. The grafted side chains of PNIPAAm were then crosslinked with gamma radiation to give net-[PP-g-NIPAAm]. The secondary network was obtained in situ by chemical crosslinking between PNAS and polylysine (pLys). The PP-g-IPNs exhibited the lower critical solution temperature (LCST) at around 32 °C. Based on its thermoreversible behavior, this system could be used for immobilization of biomolecules. The phase transition temperature (LCST) and network properties of the IPNs were measured by swelling behavior. Additional characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared (FTIR-ATR) determinations are reported. 相似文献
Poly(N-isopropyl acrylamide) (PNIPAAm) was grafted on a polysulfone UF membrane. The changes of permeability as well as retention of PEG (35 kg/mol) and Dextran (500 kg/mol) between 23 and 60 °C were determined for both grafted and unmodified membranes. The results showed that the viscosity corrected water permeability and solute retention were almost constant for the unmodified membranes within the measured temperature range, the permeability of the grafted membranes increased and the retention of Dextran and PEG decreased with temperature. The variation of changes was most obvious in the temperature range 27–37 °C for the modified membranes due to the lower critical solution temperature (LCST) of PNIPAAm. The location and profile of PNIPAAm inside and on the surface of the membrane were analysed by SEM and FTIR. Depth profile calculation for FTIR spectra showed that PNIPAAm was mostly placed inside the membrane (at a depth of 1.06–1.10 μm from the surface) rather than on the surface. The amount of grafted PNIPAAm was low and did not significantly affect the morphology of the membrane. Therefore, a difference in SEM pictures of modified and unmodified membranes could not be seen. The modified membrane exhibited a clearly different thermal response compared to the unmodified one. 相似文献
We investigated the dynamics of head-on collisions between a moving droplet and a stationary droplet on a surface with a wettability gradient. The mixing of fluids is achieved passively through convective mass transfer caused by the release of surface energy during coalescence, and also through diffusive mass transfer. The coalescence dynamics were visualized with a high-speed camera; the internal flow patterns were resolved with measurement of micro-PIV (particle image velocimetry). The results show that the released surface energy creates a pair recirculation flow inside the merged droplet when the stationary droplet is placed near the gradient, whereas most released surface energy is converted into oscillation when the stationary droplet is far from the gradient. This distinction is attributed to the motion of the contact line during coalescence. The mixing of fluorescently labeled oligonucleotides in these two modes is revealed with confocal micro-laser induced fluorescence technique. The results of 3D scans demonstrate that the motion of the contact line during coalescence distributes the fluids in a complicated manner, thus beneficial for mixing. This mechanism of enhanced mixing is applicable also for platforms other than a surface with a wettability gradient; prospective applications include improving the mixing of biochemical fluids. 相似文献
Summary: Robust thermosensitive PAH‐g‐PNIPAAm/PSS particles were prepared by addition of a poly(allylamine)‐graft‐poly(N‐isopropylacrylamide) particle suspension into poly(styrene sulfonate) solution above the LCST of PAH‐g‐PNIPAAm. Scanning force microscopy revealed stable and well‐separated particles in water at room temperature. The zeta‐potential showed a negative surface charge of the particles. Their thermosensitive behavior was demonstrated by dynamic light scattering. The release of rhodamine 6G loaded particles could respond to the incubation temperature.
Fabrication of thermosensitive and robust particle by suspension of in situ formed PAH‐g‐PNIPAAm particle above the LCST in PSS solution. 相似文献
Thermo-sensitive porous hydrogels composed of interpenetrated networks (IPN) of alginate-Ca2+ and PNIPAAm have been obtained. The hydrogels were prepared by cross-linking alginate-Na+ with Ca2+ ions inside PNIPAAm networks. Compressive tests and scanning electron microscopy were used to evaluate gel strength and pore morphology, respectively. IPN hydrogels displayed two distinct pore morphologies under thermal stimuli. Below 30-35 °C, the LCST of PNIPAAm in water, IPN hydrogels were highly porous. The pore size of hydrogel heated above LCST became progressively smaller. Alginate-Ca2+ and PNIPAAm hydrogels, used as references, did not present such behaviour, indicating that the porous effect is due to IPN hydrogel. It was verified that higher strength is achieved when the hydrogel presents small pore size and the temperature is increased. It is suggested that at temperatures above LCST, the PNIPAAm chains shrink and pull the alginate-Ca2+ networks back. During shrinking, the polymer chains occupy the open spaces (pores from which water is expelled), and therefore, the hydrogel becomes less deformable when subjected to compressive stress. The results presented in this work indicate that the mechanical properties as well as the pore morphologies of these IPN hydrogels can be tailored by thermal stimulus. 相似文献
Films of PP and PTFE were modified by gamma-radiation grafting of pH and thermo sensitive monomers (two step method) by using
both the preirradiation and the direct methods. The effects of the absorbed dose, monomer concentration and reaction time
were investigated. The surface chemistry of grafted samples was analyzed by FTIR-ATR spectroscopy, while their thermal properties
were analyzed by TGA and DSC. The stimuli-responsive behavior was studied by swelling and contact angle in water, as well
as by DSC. Sensitive films presented a critical pH and LCST. 相似文献