Fluorescent Carbon Particles formed from Concentrated Glucose Solutions
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.32
Fluorescent Carbon Particles formed from Concentrated Glucose Solutions Tomilola Obadiya, Harsh Uppala and David Sidebottom Dept. of Physics, Creighton University, 2500 California Plaza, Omaha, NE 68178, U.S.A.
Abstract Simple glucose solutions were heat treated in an attempt to produce carbon nanodots (CNDTs) with a monodisperse size distribution using a bottom-up approach. Absorption and fluorescence properties of the heat-treated solutions display remarkable similarity to CNDTs reported in the literature. However, particle-sizing and AFM measurements indicate the increasing fluorescence is accompanied by the growth of particles that are larger than most CNDTs discussed in the literature (a concentrated population of monodisperse 30 nm particles and a low concentration of much larger, roughly 500 nm, particles). A dialysis study, shows these larger particles are not responsible for the bulk of the optical properties but, rather the optical properties likely stem from molecular by-products that accompany the heating and caramelization of the sugar.
INTRODUCTION Many research groups have recently reported the production of CNDTs in a bottom up approach involving the thermal treatment of any variety of carbohydrates[15]. These studies routinely report two absorption bands at approximately 230 and 280 nm which have been associated[6] with transitions from to (at 230 nm) and from surface defect states to (at 280 nm), as well as a unique excitation-dependent fluorescence that is a hallmark[7] of CNDTs produced by more traditional top-down approaches (e.g., laser ablation)[3,7,8]. The benefit of bottom-up approaches include simple synthesis protocols that are inexpensive and can result in mass production of CNDTs in rapid fashion. From an application perspective, the fluorescence rivals that of conventional semi-conductor based quantum dots (QDs) yet CNDTs are far less toxic and have the potential to replace QDs in many bioimaging applications[7]. Inspired by previous light scattering studies of glucose solutions[9,10] which revealed the formation of monodisperse clusters of glucose forming in water with a particle size that varies from 1 to 100's nm over a concentration range of 5 to 80 wt% glucose, we investigated what happens when these cluster solutions are heated to form carbon particles. Our hope was that the resulting carbon particles would mimic the size
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of the precursor sugar clusters so that the final morphology could be controlled simply by altering the glucose concentration. EXPERIMENT Glucose solutions with a concentration 60 wt% were produced by combining D-glucose (Fisher) and MillipureTM water in a beaker and mixing with a magnetic stirrer until a transparent liquid was obtained. Based on earli
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