Thermoresponsive Fluorescent Sensor Based on Core/Shell Nanocomposite Composed of Gold Nanoparticles and Poly(N-isopropylacrylamide)

Abstract

We developed a new thermometric fluorescent sensor based on core/shell nanocomposite composed of gold nanoparticles and thermoresponsive poly(N-isopropylacrylamide), which shows a reversible fluorescence change in response to a temperature change.

Development of highly thermoresponsive fluorescent sensors consisting of plasmonic silver nanoprisms and poly(N-isopropylacrylamide)–fluorophore composites

“…The fluorescence intensity ratios below and above the LCST for previously reported metal nanoparticle-based thermoresponsive sensors range within 1.4-3.7. [8][9][10][11][12] On the other hand, the ratio obtained in the current study was 6.4, signifying that our metal nanoparticle-based fluorescent sensors show higher thermoresponsivity. The large fluorescence change is possibly due to two factors that may lead to the effective enhancement and/or quenching of the fluorescence from FITC.…”

“…1(A)). 8 Briefly, a 2.0 mg mL −1 aqueous solution of α-carboxyl ω-terminated PNIPAm (M w = 37 500; 4 mL, Polymer Source) was added to the AgPR solution (2 mL), followed by stirring for 12 h. Centrifugation (14 000 rpm; 20 min) was then repeated three times to remove the excess of free PNIPAm and the resulting precipitate was redispersed in an equivalent volume of ultrapure water to afford PNIPAm-modified AgPRs.…”

“…An aqueous solution of fluorescein isothiocyanate (FITC)-PNIPAm conjugates was prepared by adding 12.8 mM FITC in ethanol-ultrapure water (1/1 v/v, 200 μL) and a 4 mg mL −1 aqueous solution of amino-terminated PNIPAm (M w = 1000; 1.46 mL, Polymer Source) to 0.1 M carbonate buffer ( pH 9.6, 2.5 mL), followed by stirring for 6 h. 8 The conjugate solution (2 mL) was then added to a solution of PNIPAm-modified AgPRs (1 mL), followed by stirring at 20 °C for 2 h. Then, the solution was heated to 30 °C for 2 h and cooled to 20 °C for an additional 2 h under stirring to obtain FITC-PNIPAm-modified AgPR hybrids (FITC/PNIPAm/AgPRs) (Fig. 1(A)).…”

“…1,2 While various types of thermometers have been developed, [3][4][5][6][7] thermoresponsive fluorescent sensors consisting of fluorophores, thermoresponsive polymers, and metal nanoparticles have been identified to show tremendous potential as new nanosized thermometers. The mechanism of these sensors is suggested to be either energy transfer from photoexcited fluorophores to Au nanospheres 8,9 or fluorescence enhancement of the constituent fluorophores. The enhancement was induced by the generation of local electric fields along with the excitation of the localized surface plasmon resonance (LSPR) of the Ag nanospheres.…”

“…Poly(N-isopropylacrylamide) (PNIPAm), which undergoes a large volume-phase transition around the lower critical solution temperature (LCST), has been employed as an adjustable spacer between the fluorophores and the surface of the metal nanoparticles. [8][9][10][11][12] However, the resulting sensors were only moderately thermoresponsive with the differences in fluorescence intensity accompanying the LCST phase transition being less than a factor of four. This is probably because the LSPR band from the Ag nanospheres did not effectively overlap with the bands from the fluorophores.…”