Gold Nanospheres Assembled on Hydrogel Colloids Display a Wide Range of Thermoreversible Changes in Optical Bandwidth for Various Plasmonic-Based Color Switches

Abstract

An approach is presented that permits wide and reversible control of the optical bandwidth of spherical gold nanoparticles assembled on thermoreversible hydrogel colloids for various plasmonic-based thermochromisms. Temperature-dependent swelling and shrinking behaviors of the hydrogel colloids in aqueous systems manipulated assembly structures and optical signals of gold nanoparticles in the hybrid colloids. The optical bandwidths of the hybrid colloids increased with temperature, and thermoreversible bandwidth variations of the hybrid colloids were increased with the diameter of gold nanoparticles (from 15 to 51 nm). These hybrid colloids exhibited multiple colors switching during temperature changes (maximum four colors: wine ↔ violet ↔ dark blue ↔ faint blue). For the hybrid colloids showing a small bandwidth variation, another method was introduced to display different color switching.

Exploiting Metallophilicity for the Assembly of Inorganic Nanocrystals and Conjugated Organic Molecules

“…The enhancement of interparticle SPR coupling originating the red shift and broadening of the SPR band at pH 7-8 can be mainly associated to an increase of aurophilic interactions in the NCP, since no significant shrinkage or variation of size of the aggregates is observed by DLS measurements in samples at different pH ( Figure S3). 17,30 Although these results confirm the key role of metallophilic bonds in the system, the interaction of the surface atoms of Au NPs with complex 1 through the pyridinic nitrogen atom of the latter should not be neglected: the successful transfer of metallic nanostructures from organic solvents to water solutions by means of only-organic pyridine derivatives has been previously reported by other authors.…”

“…Consequently,t he observed pHdependento pticalp roperties are most likely linked to as ubtle enhancement in interparticle interactions by strengthening specific chemical bonds than to an enhancement in interparticle interactions inducedb yl arge conformational or morphological changes of the aggregates. [15,27] Interestingly, in the UV/ Vis spectra of water solutions of free complex 1 (withoutN Ps) at pH 7-8 (see Figure S11) there is notable intensification of the broad and weak band at l = 300 nm, assigned to aurophilic interactions, [28] which indicates better capacity of complex 1 to create Au I ÀAu I bonds at this pH. Indeed, for the NCP sample, the ratio of absorption intensities at l = 300 and 260 nm (A 300 /A 260 )i sm aximum at pH 7-8, andt his confirms the presence of ah igher amount of aurophilic interactions under these specific conditions ( Figure S12).…”

“…12,13 Inorganic NPs might then be 3 embedded in these supramolecular systems. 14 When polymeric or small organic molecule gelators are used for this purpose, the organic-inorganic interface is usually based on covalent bonds, 15,16 electrostatic interactions, 17 and/or hydrogen bonding. 18 The use of metallogelators instead of only-organic gelators for the formation of either hydrogels or organogels has recently become the subject of study.…”

Tunable Colloidal Crystalline Patterns on Flat and Periodically Micropatterned Surfaces as Antireflective Layers and Printable–Erasable Substrates

“…The FFT pattern (Figure c) of Figure a also suggests that the hybrid pattern had a high crystalline order. Since the surfaces of gold nanoparticles are stabilized by citrate ions, they can be electrostatically attracted by the positively charged hydrogel colloids, while having a repulsive interaction with the negatively charged silicon wafer surfaces (Si/SiO 2 ). As a result, it was possible to achieve the assembly of gold nanoparticles only on the surface of hydrogel colloids without cleaning the substrate.…”

“…Fabrication of Nonclose‐packed Hybrid Colloidal Crystal Patterns : First, 38 nm (diameter) spherical gold nanoparticles were synthesized using the methods described in literatures . For the synthesis of 15 nm spherical gold nanoparticles, 99 mL of Na 3 citrate aqueous solution (0.025 wt%) was heated to equilibrate at 100 °C for 40 min, and then 1 mL of 25 × 10 −3 m HAuCl 4 aqueous solution was added to the Na 3 citrate aqueous solution under stirring.…”