Light emission at approximately 415 nm was observed for gold particles with diameters of 2.6-6.0 nm dispersed in a solution containing bis(2,4,6-trichlorophenyl) oxalate and hydrogen peroxide. It was found that the light intensity was independent of the protecting reagents of the gold nanoparticles with similar size, the light intensity with gold nanoparticles of 5.0 and 6.0 nm in diameter was stronger than that with gold nanoparticles of 2.6 and 2.8 nm in diameter, and the light intensity increased linearly with the concentration of the gold nanoparticles using 6.0-nm gold nanoparticles. The gold nanoparticles were identified as emitting species, and the quantum yield was determined to be (2.8 +/- 0.3) x 10(-5) using 6.0-nm gold nanoparticles. The light emission is suggested to involve a sequence of steps: the oxidation reaction of bis(2,4,6-trichlorophenyl) oxalate with hydrogen peroxide yielding an energy-rich intermediate 1,2-dioxetanedione, the energy transfer from this intermediate to gold nanoparticles, and the radiative relaxation of the as-formed exited-state gold nanoparticles. The observed luminescence is expected to find applications in the field of bioanalysis owing to the excellent biocompatibility and relatively high stability of gold nanoparticles.

The reaction of gold nanoparticles with a potassium periodate-sodium hydroxide-carbonate system undergoes chemiluminescence with three emission bands at 380-390, 430-450, and 490-500 nm, respectively. It was found that the light intensity increased linearly with the concentration of the gold nanoparticles, and the CL intensity increased dramatically when the citrate ions on the nanoparticle surface were replaced by SCN(-). The shape, size, and oxidation state of gold nanoparticles after the chemiluminescent reaction were characterized by UV-visible absorption spectrometry, transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS). Gold nanoparticles are supposed to function as a nanosized platform for the observed chemiluminescent reactions. A chemiluminescent mechanism has been proposed in which the interaction between free CO(3)(*-) and O(2)(*-) radicals generated by a KIO(4)-NaOH-Na(2)CO(3) system and gold nanoparticles results in the formation of emissive intermediate gold(I) complexes, carbon dioxide dimers, and singlet oxygen molecular pairs on the surface of the gold nanoparticles. This work is not only of great importance for gaining a better understanding of the unique optical and surface properties and chemical reactivity of nanoparticles but also of great potential for developing new biosensing and immunolabeling technologies.

The effect of pH on inhibition and enhancement of luminol-H2O2-Co2+ chemiluminescence (CL) by 18 phenolic compounds and 20 amino acids was studied. It was found that most of the tested compounds showed an inhibiting effect at lower pH and an enhancing effect at higher pH. At a midrange pH, for some phenolic compounds with two ortho-position -OH, both an inhibiting and an enhancing peak were simultaneously observed. UV-visible spectra of the tested phenolic compounds at different pH values were studied. The mechanism for CL inhibition and enhancement was proposed. It is likely that the competition of the -OH or the -NH2 group and other reducing groups in the molecules with luminol for O2*- led to the CL inhibition. A reaction of -COO(-) and quinone or ketone formed by phenolic compounds at higher pH via deprotonation with O2*- also resulted in the CL enhancement.

The effect of 30 phenols and anilines on typical Ru complex electrochemiluminescence (ECL) was systematically investigated under different conditions. It was found that all the tested compounds showed an ECL inhibiting signal. The magnitude of ECL inhibition was related to the position of the substituting group in the benzene ring and decreased in the following order: meta-> ortho-> para-. The oxidation potential of the tested compounds, the ECL spectra and UV-visible absorption spectra of Ru(bpy) 2þ 3 /tripropylamine (TPrA) in the presence of phenols and anilines, and the direct ECL between Ru(bpy) 2þ 3 and phenols/aniline were studied. The mechanism of ECL inhibition has been proposed due to energy transfer from the excited state Ru(bpy) system, respectively.

It was found that potassium permanganate (KMnO(4)) could react with gold nanoparticles in a strong acid medium to generate particle size-dependent chemiluminescence (CL). For gold nanoparticles with the size of 2.6 or 6.0 nm, the reaction was fast and could produce the excited state Mn(II) with light emission around 640 nm. For gold nanoparticles larger than 6.0 nm, no light emission was observed due to a much slower reaction rate. The CL intensity was found to increase linearly with the concentration of 2.6 nm gold nanoparticles. The effects of the acid medium, concentration of KMnO(4) and presence of N(2) and O(2) were investigated. UV-Vis absorption spectra and X-ray photoelectron spectra (XPS) measured before and after the CL reaction were analyzed. A CL mechanism has been proposed suggesting that the potassium permanganate was reduced by gold nanoparticles in the strong acid medium to the excited state Mn(II), yielding light emission. The results bestow new light on the size-dependent chemical reactivities of the gold nanoparticles and on nanoparticle-induced chemiluminescence. The CL reaction was considered to be of potential use for bioanalysis applications.