A Cooperative Effect of Bifunctionalized Nanoparticles on Recognition:  Sensing Alkali Ions by Crown and Carboxylate Moieties in Aqueous Media

• Published in: Analytical chemistry (Washington) Vol. 77; no. 15; pp. 4821 - 4828
• Main Authors: Lin, Shu-Yi, Chen, Chun-hsien, Lin, Meng-Chieh, Hsu, Hsiu-Fu
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.08.2005
• Subjects: Analytical chemistry; Aqueous solutions; Chemistry; Exact sciences and technology; Gold; Nanoparticles; Sensitivity analysis; Sensors; Spectrometric and optical methods; Performance evaluation; Human; Urine; Complexation; Gold; Nanoparticle; Potassium ion; Chain length; Bifunctional compound; Atomic emission spectrometry; Crown compound; Surface plasmon; Inductive coupling plasma spectrometry; Chemical enrichment; Efficiency; Sodium ion; Carboxylate; Rate constant; Functional group; Ultraviolet visible spectrometry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac050443r

Reported here is a cooperative effect that the sensing efficiency of the active group on gold nanoparticles (GNPs) can be significantly influenced by another proximal functional group. We previously developed a visual sensing scheme for K+ by 15-crown-5-CH2O(CH2)12SH functionalized GNPs in aqueous matrix. Upon adding K+, the GNP solution changes from red to blue. Such a transform is triggered by a 2-to-1 sandwich complexation of crown to K+, resulting in the red shift of surface plasmon absorption due to GNP aggregation. Herein, we discover that introducing a second functionality, thioctic acid (TA), onto GNPs significantly affects the sensing efficiency of crown moieties (15-crown-5-CH2O(CH2) n SH and 12-crown-4-CH2O(CH2) n SH, where n = 4, 8, and 12). The rate constant of K+ recognition by TA- and 15-crown-5-CH2O(CH2)4S-bifunctionalized GNPs is more than 4 orders of magnitude faster than the others containing longer methylene chains. The same chain-length dependence is also found in the case of Na+ sensing by 12-crown-4 functionalized GNPs. The discrepancy in sensing performance is attributed to a cooperative effect that the negatively charged carboxylate of TA may preorganize the crown moiety for K+ recognition. This method is applied to measure K+ and Na+ in human urine by UV−visible spectrometry. By adjusting the concentrations of GNPs, the dynamic ranges tuned for K+ and Na+ are, respectively, 6.25 μM−1.12 mM and 0.156−4.00 mM, suitable for real samples pretreated simply by 10-fold dilution. The results ([K+] = 20.3 mM, [Na+] = 45.1 mM) agree with those obtained from ICP-AES ([K+] = 19.8 mM, [Na+] = 43.8 mM).