Lysozyme-stabilized Ag nanoclusters: synthesis of different compositions and fluorescent responses to sulfide ions with distinct modes

Abstract

In this study, three kinds of red-emitting Ag nanoclusters capped with denatured lysozyme (dLys-AgNCs) were synthesized from different reactant molar ratio of AgNO 3 and lysozyme, called dLys-AgNCs 1, dLys-AgNCs 2 and dLys-AgNCs 3, respectively.The thus synthesized dLys-AgNCs 1 contained only Ag(0), while dLys-AgNCs 2 and dLys-AgNCs 3 contained both Ag(0) and Ag(I). The maximum emission wavelengths of the three dLys-AgNCs were all located near 640 nm when excited at 490 nm, but with different photoluminescence intensity. The photoluminescence properties of these dLys-AgNCs in the presence of common inorganic anions were studied. The three dLys-AgNCs had distinct photoluminescence responding mode to S 2-. The photoluminescence of dLys-AgNCs 1 could be quenched by S 2-, as S 2-destroyed the nanostructure of dLys-AgNCs 1 by forming Ag 2 S. While, the photoluminescence of dLys-AgNCs 3 could be enhanced by S 2-, as S 2-would combine with Ag(I) contained in dLys-AgNCs 3 and altered the ligand-to-metal-metal charge transfer process. For dLys-AgNCs 2, the photoluminescence was enhanced firstly with small amount of S 2-and then quenched with more S 2-added, and this could be due to that S 2-combined with Ag(I) first at low concentration and then with Ag(0) in high concentration. Other anions had no obvious effects except that I -could quench the photoluminescence of these three dLys-AgNCs. The responding mechanisms were further studied by XPS, MS, zeta potential, DLS, and lifetime measurements. Moreover, the as-prepared dLys-AgNCs 1 and dLys-AgNCs 3 were used as fluorescent probe for S 2-

Photoluminescence Mechanisms of Dual-Emission Fluorescent Silver Nanoclusters Fabricated by Human Hemoglobin Template: From Oxidation- and Aggregation-Induced Emission Enhancement to Targeted Drug Delivery and Cell Imaging

“…Interestingly enough, in contrast to Hb, using such proteins as BSA, HSA, , Lys, , and dBSA as capping agents needs the addition of a hazardous additive and/or NaBH 4 as a strong reducing agent and results in the formation of a single silver cluster size. These phenomena may be due to (i) the extraordinary flexibility of the Hb structure; (ii) the high amine/thiol ratio in Hb (94/6) compared to BSA (102/35) and Lys (18/8), which allow an effective coordination of Ag ions; and (iii) the reduction of Ag ions with 18 tyrosine/tryptophan residues in alkaline media according to its p K a (∼10), resulting in the formation of stable luminescent Hb/AgNCs in an aqueous solution. ,, The other interesting finding was to shorten the reaction time by increasing the temperature from 27 to 67 °C (Figure S6) so that the maximum emission intensity for both wavelengths (450 nm/760 nm) was recorded at 67 °C until 10 days, with similar characterization regarding low temperature synthesis (Figure e and f).…”

“…Interestingly enough, in contrast to Hb, using such proteins as BSA, 46 HSA, 13,47 Lys, 48,49 and dBSA 50 as capping agents needs the addition of a hazardous additive and/or NaBH 4 as a strong reducing agent and results in the formation of a single silver cluster size. These phenomena may be due to (i) the extraordinary flexibility of the Hb structure; (ii) the high amine/thiol ratio in Hb (94/6) compared to BSA (102/35) and Lys (18/8), which allow an effective coordination of Ag ions; and (iii) the reduction of Ag ions with 18 tyrosine/ tryptophan residues in alkaline media according to its pK a (∼10), resulting in the formation of stable luminescent Hb/ AgNCs in an aqueous solution.…”

Ratiometric Fluorescent Biosensing of Hydrogen Peroxide and Hydroxyl Radical in Living Cells with Lysozyme–Silver Nanoclusters: Lysozyme as Stabilizing Ligand and Fluorescence Signal Unit

“…Water-soluble metallic nanoclusters (MNCs), famous for their intrinsic values such as facile synthesis, ultrafine size, and excellent biocompatibility, − have been well employed for fluorescence sensing platforms. − In the procedures of MNCs synthesis, ligands are needed to protect MNCs against aggregation. Among various ligands, proteins are considered as ideal candidates because nanoclusters capped with proteins possesses excellent biocompatibility and very stable optical properties. , Ratiometric fluorescence probes for H 2 O 2 detection based on MNCs have been reported, wherein proteins were modified with organic fluorescent molecules and then served as ligands to synthesize MNCs. , In such a strategy, MNCs acted as reference signal, whereas organic molecules which were susceptible to H 2 O 2 served as response signal. Nonetheless, complicated modification of fluorophores and tedious synthetic procedures were inevitable in the construction of this kind of ratiometric sensors.…”

“…Among various ligands, proteins are considered as ideal candidates because nanoclusters capped with proteins possesses excellent biocompatibility 26 and very stable optical properties. 27,28 Ratiometric fluorescence probes for H 2 O 2 detection based on MNCs have been reported, wherein proteins were modified with organic fluorescent molecules and then served as ligands to synthesize MNCs. 29,30 In such a strategy, MNCs acted as reference signal, whereas organic molecules which were susceptible to H 2 O 2 served as response signal.…”

Luminescent Metal Nanoclusters for Potential Chemosensor Applications

“…The recognition of S 2− ions also revealed fluorescent quenching with an LOD of 2 nM. Gao et al performed S 2− ion detection by utilizing denatured lysozyme-capped clusters (dLys-Ag NCs) [99]. They tuned the molar ratios of AgNO 3 to lysozyme (1:1, 2:1, and 4:1 for synthesizing dLys-Ag NCs 1, 2, and 3, respectively) and then used them in sensor titrations.…”