Increasing efforts are directed to the application of metal and semiconductor nanoparticles (NPs) for the development of electronic or optical sensory systems.[1] Metal or semiconductor NPs functionalized with nucleic acids were employed as amplifying labels for the detection of DNA; the dissolution of the nanoparticles was used to follow DNA hybridization events.[2] Also, charge injection from semiconductor nanoparticles into electrodes and the generation of photocurrents was used to follow hybridization processes [3] and biocatalytic transformations.[4] The catalytic deposition of metals onto metal nanoparticles conjugated to DNA-hybridized complexes on surfaces was used as a sensor for DNA through conductivity [5] or microgravimetric quartz crystal microbalance [6] measurements. The optical detection of processes in the presence of metal and semiconductor NPs has become a common practice in analysis. Besides the use of semiconductor quantum dots as fluorescence labels in sensors, [7] the fluorescence quenching of semiconductor quantum dots has been employed in different sensing paths.[8] The plasmon absorbance of metal nanoparticles, such as Au NPs, and specifically the interparticlecoupled plasmon absorbance of aggregated NPs was extensively used to follow molecular [9] and biomolecular [10] recognition processes. The use of semiconductor or metallic NPs as probes to follow biocatalytic processes is less established, with only a few reports for these applications. [4,11] Nicotinamide adenine dinucleotide (NAD + )-and nicotinamide adenine dinucleotide phosphate (NADP + )-dependent enzymes are important in biocatalyzed synthesis.[12] Extensive efforts have been directed towards the development of electrochemical sensors based on NAD(P) + -dependent enzymes.[13] Herein, we report the catalyzed growth of gold nanoparticles in the presence of NAD(P)H cofactors. We apply the process to the quantitative optical analysis of NAD(P)H cofactors and to the analysis of NAD(P) + -dependent biocatalyzed reactions in solutions and on surfaces.The solution for the growth of the particles consisted of citrate-stabilized Au NPs (4.0 10 À10 m in 13 nm AE 1-nm particles), HAuCl 4 (1.8 10 À4 m), and CTAB (7.4 10 À2 m) as a surfactant. Figure 1 shows the changes in the UV/Vis spectra of the growth solution upon interaction with different concentrations of NADH. In the absence of NADH, the solution displays an absorbance band at l = 392 nm, characteristic of the AuCl 4 À component (Figure 1, curve a). Upon addition of NADH, this band disappears instantaneously and the characteristic orange color of the system is depleted (curve b), and then the slow buildup of the absorbance of the particle plasmon is observed. As the concentration of NADH increases, the absorbance of the Au particles increases and is shifted to longer wavelengths (from 523 to 530 nm; Figure 1, curves c-h). The inset in Figure 1 shows the calibration curve derived from the changes in the absorbance at l = 524 nm as the concentration of NADH increases. Figure 2 shows...
Increasing efforts are directed to the application of metal and semiconductor nanoparticles (NPs) for the development of electronic or optical sensory systems.[1] Metal or semiconductor NPs functionalized with nucleic acids were employed as amplifying labels for the detection of DNA; the dissolution of the nanoparticles was used to follow DNA hybridization events.[2] Also, charge injection from semiconductor nanoparticles into electrodes and the generation of photocurrents was used to follow hybridization processes [3] and biocatalytic transformations.[4] The catalytic deposition of metals onto metal nanoparticles conjugated to DNA-hybridized complexes on surfaces was used as a sensor for DNA through conductivity [5] or microgravimetric quartz crystal microbalance [6] measurements. The optical detection of processes in the presence of metal and semiconductor NPs has become a common practice in analysis. Besides the use of semiconductor quantum dots as fluorescence labels in sensors, [7] the fluorescence quenching of semiconductor quantum dots has been employed in different sensing paths.[8] The plasmon absorbance of metal nanoparticles, such as Au NPs, and specifically the interparticlecoupled plasmon absorbance of aggregated NPs was extensively used to follow molecular [9] and biomolecular [10] recognition processes. The use of semiconductor or metallic NPs as probes to follow biocatalytic processes is less established, with only a few reports for these applications. [4,11] Nicotinamide adenine dinucleotide (NAD + )-and nicotinamide adenine dinucleotide phosphate (NADP + )-dependent enzymes are important in biocatalyzed synthesis.[12] Extensive efforts have been directed towards the development of electrochemical sensors based on NAD(P) + -dependent enzymes.[13] Herein, we report the catalyzed growth of gold nanoparticles in the presence of NAD(P)H cofactors. We apply the process to the quantitative optical analysis of NAD(P)H cofactors and to the analysis of NAD(P) + -dependent biocatalyzed reactions in solutions and on surfaces.The solution for the growth of the particles consisted of citrate-stabilized Au NPs (4.0 10 À10 m in 13 nm AE 1-nm particles), HAuCl 4 (1.8 10 À4 m), and CTAB (7.4 10 À2 m) as a surfactant. Figure 1 shows the changes in the UV/Vis spectra of the growth solution upon interaction with different concentrations of NADH. In the absence of NADH, the solution displays an absorbance band at l = 392 nm, characteristic of the AuCl 4 À component (Figure 1, curve a). Upon addition of NADH, this band disappears instantaneously and the characteristic orange color of the system is depleted (curve b), and then the slow buildup of the absorbance of the particle plasmon is observed. As the concentration of NADH increases, the absorbance of the Au particles increases and is shifted to longer wavelengths (from 523 to 530 nm; Figure 1, curves c-h). The inset in Figure 1 shows the calibration curve derived from the changes in the absorbance at l = 524 nm as the concentration of NADH increases. Figure 2 shows...
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