Spontaneous formation of gold nanostructures in aqueous microdroplets

Abstract

The synthesis of gold nanostructures has received widespread attention owing to many important applications. We report the accelerated synthesis of gold nanoparticles (AuNPs), as well as the reducing-agent-free and template-free synthesis of gold nanoparticles and nanowires in aerosol microdroplets. At first, the AuNP synthesis are carried out by fusing two aqueous microdroplet streams containing chloroauric acid and sodium borohydride. The AuNPs (~7 nm in diameter) are produced within 60 µs at the rate of 0.24 nm µs−1. Compared to bulk solution, microdroplets enhance the size and the growth rate of AuNPs by factors of about 2.1 and 1.2 × 105, respectively. Later, we find that gold nanoparticles and nanowires (~7 nm wide and >2000 nm long) are also formed in microdroplets in the absence of any added reducing agent, template, or externally applied charge. Thus, water microdroplets not only accelerate the synthesis of AuNPs by orders of magnitude, but they also cause spontaneous formation of gold nanostructures.

Reaction of chloroauric acid with histidine in microdroplets yields a catalytic Au–(His)2complex

“…Microdroplet chemistry has emerged as a unique platform for studying and performing chemical reactions. [16][17][18][19][20][21][22] The ESI/ ESSI as the main setup to generate charged microdroplets is usually accompanied by special redox reactions, which have been used for some synthesis reaction and nanomaterials. 23,24 Microdroplets as microreactors combined with on-line MS have been used to capture and identify transient intermediates of organic reactions, and microdroplet chemistry has been broadly applied in the eld of bioanalytical detection.…”

A microdroplet-accelerated Biginelli reaction: mechanisms and separation of isomers using IMS-MS

“…Recently, the groups of Cooks, [17][18][19][20][21][22][23][24][25][26] Zare, [27][28][29][30][31][32][33][34][35][36][37][38][39] and others [40][41][42][43][44][45][46] have reported the acceleration of reactions in microdroplet environments during the process of electrospraying reagents into a mass spectrometer. 32 Intrigued by the possibility of faster rates for multicomponent reactions, we explored the use of microdroplets as a means of enabling a rapid Biginelli reaction (Scheme 2).…”

Ultrafast enzymatic digestion of proteins by microdroplet mass spectrometry

“…In the past few years, microdroplets have been extensively reported to dramatically accelerate various types of single-phase or two-phase organic reactions that have slow kinetics or need specific catalysts in the bulk phase [12][13][14] . They have also been used to study fast reaction kinetics via microdroplet fusion mass spectrometry (MS) 6,10,15,16 , to perform chemical syntheses 17 , and also to facilitate nanomaterial synthesis 11,18,19 . The exact reasons for the reaction rate acceleration in microdroplets have not been clearly established, but it is commonly believed that it is caused mainly by the sharp difference between the environments of microdroplets and the corresponding bulk phase 20 .…”