Kwanyeol Paek

Efficient colorimetric pH sensor based on responsive polymer-quantum dot integrated graphene oxide.

In this paper, we report the development of a versatile platform for a highly efficient and stable graphene oxide (GO)-based optical sensor that exhibits distinctive ratiometric color responses. To demonstrate the applicability of the platform, we fabricated a colorimetric, GO-based pH sensor that responds to a wide range of pH changes. Our sensing system is based on responsive polymer and quantum dot (QD) hybrids integrated on a single GO sheet (MQD-GO), with the GO providing an excellent signal-to-noise ratio and high dispersion stability in water. The photoluminescence emissions of the blue and orange color-emitting QDs (BQDs and OQDs) in MQD-GO can be controlled independently by different pH-responsive linkers of poly(acrylic acid) (PAA) (pKa=4.5) and poly(2-vinylpyridine) (P2VP) (pKa=3.0) that can tune the efficiencies of Förster resonance energy transfer from the BQDs to the GO and from the OQDs to the GO, respectively. As a result, the color of MQD-GO changes from orange to near-white to blue over a wide range of pH values. The detailed mechanism of the pH-dependent response of the MQD-GO sensor was elucidated by measurements of time-resolved fluorescence and dynamic light scattering. Furthermore, the MQD-GO sensor showed excellent reversibility and high dispersion stability in pure water, indicating that our system is an ideal platform for biological and environmental applications. Our colorimetric GO-based optical sensor can be expanded easily to various other multifunctional, GO-based sensors by using alternate stimuli-responsive polymers.

Fluorescent and pH-responsive diblock copolymer-coated core–shell CdSe/ZnS particles for a color-displaying, ratiometric pH sensor

A color distinctive, ratiometric pH sensor was demonstrated using pH responsive and fluorescent (PyMMP-b-P2VP) diblock copolymer coated CdSe/ZnS QDs. Due to the change in the P2VP conformations in response to pH change, the color of QDs in solution changes distinctly from blue to red.

Precise control of quantum dot location within the P3HT-b-P2VP/QD nanowires formed by crystallization-driven 1D growth of hybrid dimeric seeds.

Herein, we report a simple fabrication of hybrid nanowires (NWs) composed of a p-type conjugated polymer (CP) and n-type inorganic quantum dots (QDs) by exploiting the crystallization-driven solution assembly of poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) rod-coil amphiphiles. The visualization of the crystallization-driven growth evolution of hybrid NWs through systematic transmission electron microscopy experiments showed that discrete dimeric CdSe QDs bridged by P3HT-b-P2VP polymers were generated during the initial state of crystallization. These, in turn, assemble into elongated fibrils, forming the coaxial P3HT-b-P2VP/QDs hybrid NWs. In particular, the location of the QD arrays within the single strand of P3HT-b-P2VP can be controlled precisely by manipulating the regioregularity (RR) values of P3HT block and the relative lengths of P2VP block. The degree of coaxiality of the QD arrays was shown to depend on the coplanarity of the thiophene rings of P3HT block, which can be controlled by the RR value of P3HT block. In addition, the location of QDs could be regulated at the specific-local site of P3HT-b-P2VP NW according to the surface characteristics of QDs. As an example, the comparison of two different QDs coated with hydrophobic alkyl-terminated and hydroxyl-terminated molecules, respectively, is used to elucidate the effect of the surface properties of QDs on their nanolocation in the NW.

Multicolor Emission of Hybrid Block Copolymer–Quantum Dot Microspheres by Controlled Spatial Isolation of Quantum Dots

Multicolor or white light-emitting systems have attracted great attention because of their potential uses as lighting sources and full-color displays. [ 1 ] In recent years, numerous efforts have been devoted to the development of low-cost, simple processes for the fabrication of pure white-light sources as an alternative for conventional lighting sources. [ 2–4 ] Fluorescent quantum dots (QDs) have been explored as one of the promising candidate materials due to their pure color emission spectra, high fl uorescence quantum yield, and photochemical stability. [ 5 , 6 ] However, the emission spectrum produced by each individual QD is narrow, thus requiring simultaneous emission from more than two colored QDs to illuminate across the visible regime. Typically, this is achieved through a combination of either three different QDs emitting red, green and blue light or two different ones emitting orange/red and green/blue light. In such a system, undesired Förster resonance energy transfer (FRET) between QDs often occurs, decreasing the effi ciency of the white light emission. [ 7 , 8 ] The controlled spatial isolation of multiple QDs is made necessary by the strong dependence of the energy-transfer process on the donor-acceptor distance on the nanometer scale. [ 9 , 10 ]

Efficient temperature sensing platform based on fluorescent block copolymer-functionalized graphene oxide.

Efficient temperature-sensing platform was demonstrated using temperature-responsive, fluorescent P7AC-b-PNIPAM-b-PSN3 block copolymer-anchored graphene oxide sheets (FGO). FGO exhibited extraordinary stability in water and showed fast optical on-off switching behavior in response to temperature change.