Simple and Selective Sensing of Cysteine Using Gold Nanoparticles Conjugated with a Thermoresponsive Copolymer Having Carboxyl Groups

Abstract

We describe a simple, yet selective cysteine sensor based on gold nanoparticles (AuNPs) conjugated with thermoresponsive copolymers, the carboxyl groups of which are incorporated. Copolymer-conjugated AuNPs, used as the cysteine sensor, in a solution form sediment when cysteine is added. Heating followed by cooling the solution induces phase transitions of the thermoresponsive copolymers, resulting in an acceleration of sedimentation of the copolymer-conjugated AuNPs. The absorbance of supernatants at 520 nm, which are ascribed to a surface plasmon band of discrete AuNPs, decays with increasing concentration of cysteine. Sedimentation of the copolymer-conjugated AuNPs is specific to cysteine. The addition of other popular amino acids, or ascorbic acid, causes no sedimentation of the AuNPs. The relationship between the absorbance of the supernatant at 520 nm and the cysteine concentration provides a sigmoidal profile at a concentration range between 1 × 10 -6 to 6 × 10 -6 mol dm -3 . The determination of cysteine in a supplement is achieved using an inflection point on the sigmoidal profiles.

Noble Metal Nanomaterials

“…The addition of glutathione results in spontaneous disassembly of the aggregates with a concomitant colorimetric response. AuNPs conjugated with thermoresponsive copolymers have also been utilized for the colorimetric sensing of thiol compounds [254,255].…”

Release of Nile Red from Thermoresponsive Gold Nanocomposites by Heating a Solution and the Addition of Glutathione

“…The other thermoresponsive copolymers, poly(N-isopropylacrylamide(90 mol%)-co-N-acryloyltryethylenetetramine (10 mol%)) (p(NIP0.9-TETA0.1)), poly(N-isopropylacrylamide (90 mol%)-co-N-methacrylate(10 mol%)) (p(NIP0.9-MA0.1)) 24 and poly(N-isopropylacrylamide) (pNIP), 3 were synthesized with corresponding monomers by radical polymerization, as reported elsewhere.…”

“…Colorimetric sensing systems have been fabricated based on colorimetric properties that can be controlled externally using thermoresponsive gold nanocomposites. [23][24][25][26] Considering these previous applications based on the versatile properties, thermoresponsive gold nanocomposites also have the potential for use as drug delivery materials and nano-actuators. In this study, we investigated the conjugation of gold nanoparticles with thermoresponsive polymers for fabricating thermoresponsive gold nanocomposites as a model of drug delivery materials and colloidal sensors.…”

Spectrophotometric Determination of Cysteine with Gold Nanoparticles Stabilized with Single-stranded Oligonucleotides

“…Therefore, the result suggested a detection limit as low as 100 nM, which is much lower than those of other AuNPs-based spectrophotometric methods. [20][21][22] To investigate the selectivity for cysteine detection with the proposed method, we also measured the influences of the other 19 essential amino acids according to the proposed analytical procedure. Figure 3B showed that the A600nm/A520nm value of cysteine was strikingly larger than those of the other 19 amino acids, indicating that the assay approach has very high specificity towards cysteine among the 20 essential amino acids.…”

“…Okubo et al constructed a cysteine sensor based on 13 nm diameter citrate-capped AuNPs conjugated with thermoresponsive copolymers, the carboxyl groups of which were incorporated. 21 The cysteine concentration could be obtained by a sigmoidal profile at a concentration range between 1 to 6 µM. Wu et al developed a sensor for detecting cysteine in a solution of 13 nm diameter fluorosurfactant-capped AuNPs.…”