Fluorescent silver nanoclusters capped by polyethyleneimine with different molecular weights: Universal synthesis and application as a temperature sensor

In this paper, we developed a universal, applicable and simple synthetic method of Ag nanoclusters capped by polyethyleneimine (PEI) with different molecular weights (AgNC-PEIs), including Mw 600, 1300, 1800, 2000, 10,000, 25,000, 70,000, and 750,000. Using formaldehyde as the sole reducing agent, silver nanoclusters could be successfully prepared by using these templates. Subsequently, several characterization techniques were employed to investigate the properties of AgNC-PEIs, and the results suggested that these AgNC-PEIs had similar sizes, structures, and optical features. However, besides the common characteristics, different temperature sensitivities were found for these nanoclusters, in which AgNC-PEI 25000 was proper to be applied as a temperature sensor. With increasing temperature, the fluorescence quenched dramatically, and this change could be readily observed by naked eyes under UV light. Injection of these temperature sensitive nanoclusters into a glass tube, a simple thermometer could be fabricated easily, thus AgNC-PEI 25000 would be a promising candidate for temperature sensing as a visible indicator.