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    Home > ACS Nano: block copolymer (BCP) particles can be used as optical sensors

    ACS Nano: block copolymer (BCP) particles can be used as optical sensors

    • Last Update: 2019-05-01
    • Source: Internet
    • Author: User
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    Sensitive detection of physiological signals (neutral pH and body temperature) plays an important role in biomedical applications In particular, the direct visualization of physiological response signals provides some ideas for tumor detection At present, stimulus responsive polymers have been widely used in the detection system under physiological conditions, but there are still some problems, such as the difficulty of polymer synthesis, poor solubility, and easy deactivation in physiological environment Therefore, it is very urgent to develop polymer particles with shape conversion as optical sensors to detect local temperature and pH changes Recently, Professor bumjoon J Kim's research group of Korea Academy of higher science and technology used random polymers deaeam and NIPAM as surfactants to construct temperature and pH responsive block copolymer (BCP) particles By optimizing the ratio of deaeam to NIPAM, the solubility of particles changes significantly in the range of ph6.0-7.0 and 30-40 ℃, so that the shape of particles changes between Rugby shape and lens shape At the same time, the incorporation of fluorescent dye makes it possible to detect the change of particle shape by colorimetry, that is to say, the change of pH and temperature by colorimetry Relevant achievements were published on ACS Nano under the title of "shape and color switchable block polymer particles by temperature and pH dual responses" (DOI: 10.1021 / acsno 8b09276) Firstly, a series of BCP particles (Figure 1a) were obtained by evaporation of emulsion droplets in solution containing PS 27k-b-p4vp 7K and deaeam-r-nipam By changing the pH and temperature of the buffer solution in the process of emulsification, the effect of the buffer solution on the shape transition of BCP particles was studied The transmission / scanning electron microscope images clearly show that PS-b-P4VP BCP particles have two kinds of structures: cylindrical lenticular and rugby (Figure 1b-d) When the pH is 6.0, only the lens structure (Figure 1b) can be observed at any temperature At pH 6.5 and 7.0, the shape of BCP particles is determined by temperature When pH is 6.5, temperature is 20 ℃ and 35 ℃, BCP particles are lenticular; when temperature rises to 50 ℃, rugby particles begin to form Similarly, when the pH is 7.0 and the temperature is 20 ℃, BCP particles are lenticular When the temperature rises to 35 ℃ or 50 ℃, rugby particles begin to form The low magnification scanning electron microscope images (Figure 1c and 1D) also confirmed the morphological transformation of all particles from rugby to lenticular shape under different temperature and pH conditions (source: ACS Nano) next, the author used a polymer (p48) containing 48 mol% NIPAM to study the effect of temperature and pH on particle shape Figure 2A summarizes the volume fractions of p48 and PS 27k-bp4vp 7K in BCP particles at different pH and temperature For BCP particles prepared at pH 6.5 and 7.0, the authors observed a significant increase in the volume fraction of p48 at critical temperatures (40-45 ° C at pH 6.5 and 30-35 ° C at pH 7.0) However, for BCP particles prepared at pH 6.0, the volume fraction of p48 is constant at 2-3% at any temperature During the emulsification process, the majority of P48 polymers migrate to the surrounding aqueous media to form cylindrical lens like particles (Figure 2b) On the contrary, when a large amount of P48 is retained in the BCP emulsion phase, a layered Rugby particle (Figure 2b) is formed (source: ACS Nano) the author further investigated the shape transition of BCP particles with simultaneous change of temperature and pH (Figure 3) The BCP particles prepared at pH 6.5 and 40 ℃ showed lenticular shape The pH value increased from 6.5 to 7.0, and the temperature was constant at 40 ℃ During the solvent annealing process, the shape transition from lenticular to rugby was produced At pH 7.0, the increased solubility of p48 in chloroform resulted in the migration of p48 from the aqueous phase to the BCP particles swelling through chloroform Then, at pH 7.0, the temperature was adjusted from 40 ℃ to 30 ℃, and the rugby particles recovered to lenticular particles More importantly, the transformation between lenticular particles and rugby particles has good reversibility (source: ACS Nano) finally, in order to explore the potential of BCP particles as an optical sensor to detect local temperature and pH changes, the author combined the fluorescent dye rhodamine B (RB) and coumarin (CM) to build a model on BCP particles With the change of particle shape and nanostructure, the fluorescence color of BCP changed from light red to blue (Figure 4A and 4B) In order to verify the reversibility of optical behavior in the process of particle shape transformation, I 600 nm / I 450 nm (Figure 4C) of BCP particles with continuous circulation at different temperature and pH were drawn When the shape of particles changed from lens to rugby, the value of I 600 nm / I 450 nm decreased from 0.52 to 0.30 In addition, this change can be repeated in repeated solvent annealing cycles (source: ACS Nano) in a word, the author developed a BCP particle whose shape and color changed with the change of physiological conditions (pH around 7.0 and temperature around 35 ˚ C) During the continuous cycle, the shape of particles changes reversibly between lens and rugby In addition, the introduction of fluorescent dyes has successfully realized the colorimetric detection of pH and temperature The polymer particles have a great prospect in the application of biomedical sensing and clinical systems.
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