Optically Active Ultrafine Au–Ag Alloy Nanoparticles Used for Colorimetric Chiral Recognition and Circular Dichroism Sensing of Enantiomers

Abstract

Despite a significant surge in the number of investigations into chirality at the nanoscale, especially thiolated chiral molecules capping gold clusters, only limited knowledge is currently available to elaborate the alloying effect on chiroptical behavior of bimetallic nanoparticles (NPs). Also, few successful cases as to the efforts toward the development of chirality-dependent applications on the optically active nanomaterial have been made. Herein, as a positive test case for chiral alloy nanoparticle synthesis, the stable and large chiroptical ultrafine Au-Ag alloy NPs were prepared by reduction of different molar fractions of HAuCl and AgNO with NaBH in the presence of d/l-penicillamine (d/l-Pen). Compared with those of monometallic Au and Ag counterparts with comparable size, the Au-Ag alloy NPs (Ag mole fraction, 70%) obviously displayed the largest optical activities with the maximum g-factors of ∼1.6 × 10. Impressively, the Pen-mediated synthesis of chiral Au-Ag alloy NPs possesses a colorimetric self-recognition function and can be used as an incisive circular dichroism (CD) probe toward d- and l-Pen enantiomers. The plasmonic CD signal amplification (ΔI) shows good linearity with the amount of Pen over the range of 5.0-80.0 μM with a detection limit (3σ) of 1.7 μM for l-Pen and 1.5 μM for d-Pen, respectively. In addition, the sensing system exhibits good selectivity toward d- and l-Pen in the presence of other enantiomers; therefore, it is highly expected that the approach described here would open new opportunities for design of more novel enantioselective analyses of important species related to biological processes.

Ultrasmall noble metal nanoparticles: Breakthroughs and biomedical implications

“…Chiral AgNCs that possess both CD and circularly polarized luminescence (CPL) signatures were reported recently, where the chirality in ligand staples likely gave rise to the chiroptical activity in the emission states[191]. Chirality is also observed in alloying (doping) UNMNPs such as Au-Pd[192–194] and Au-Ag[195–197] nanoparticles. Understanding the fundamentals of chirality in these ultrasmall nanosystems is indispensable for the advancement of future applications.…”

“…Chirality serves as an important aspect of specific molecular recognition within biosystem and is crucial for areas such as pharmaceuticals and agrochemicals. UNMNPs-based biomolecule chiral recognition and enantiomer sensing were demonstrated recently, through either the individual nanoparticles[197] or their three-dimensional assembly[214].…”

Kinetics of Spontaneous Bimetallization between Silver and Noble Metal Nanoparticles

“…Bimetallic nanoparticles (NPs) attract significant attention because they usually exhibit more interesting catalytic, [1][2][3] photocatalytic, [4] electrocatalytic, [5,6] and optical properties [7,8] than do their corresponding monometallic NPs. We previously reported that the simple physical mixture of different NP sols spontaneously leads to the formation of core/shell structured bimetallic NPs (Scheme 1) [9][10][11][12] or an ano-alloy, [13] and am ixture of palladium NPs and gold ions forms crown-jewel typeb imetallic NPs.…”

A Surface Mediated Supramolecular Chiral Phenomenon for Recognition of l- and d-Cysteine

“…Various methods have been used for the chiral recognition of enantiomers, in particular, optical methods, such as colorimetry [4,5,6,7], spectrofluorimetry [8,9,10,11] and circular dichroism (CD) spectroscopy [12,13,14,15,16,17,18] have received great interest due to their apparent advantages over other methods by virtue of their high sensitivity and the convenience in operation. CD spectroscopy is generally utilized to analyze the molecular chirality, which is sensitive to the conformational changes of the chiral molecules.…”