Spatial control of nanoreactions on cellulose nanofibers using drop evaporation

•Spatially controlling nanoreactions using drop evaporation.•Various depositions of gold nanoparticles can be modulated on cellulose nanofibers.•Fabrication of highly sensitive SERS substrates for single bacterial detection.•Bridging gaps between drop evaporation modulation and chemical reaction control. Spatial control of nanoreactions in solution holds prospects for various applications. Great efforts have been made on the exploration of control methods. However, most of them require applications of specific instruments and addition of templates/additives, as well as complicated operations, to transform the reaction from homogeneous to heterogeneous, thus limiting their potential applications. Here we report a facile but effective strategy for spatially controlling nanoreactions within a sessile drop, by simply modulating its evaporation dynamics. We take the reaction between cellulose nanofibers (CNFs) and gold precursors as an example and achieve the uniform and ring-like depositions of gold nanoparticles (AuNPs) by separately evaporating drops of mixture of CNFs and gold precursors on glass surfaces at room temperature and enhanced temperature; meanwhile, we achieve the eye-like deposition of AuNPs by evaporating the drop of gold precursors on a CNF-textured surface. We further demonstrate the applicability of this strategy to fabricate the substrate for surface enhanced Raman spectroscopy with high sensitivity and low limit of detection (down to single bacterial level). Our findings not only bridge gaps between the modulation of drop evaporation and the control of chemical reactions, but also provide a novel strategy of spatially controlling nanoreactions for a wide range of applications, e.g., sensor nanofabrication, materials chemistry, microelectronic engineering and environmental science.