Rice is staple food for people in many countries for centuries. It is therefore considered as safe and environmental friendly material for pharmaceutical formulations. In the present study, aqueous extracts of three different parts of rice grain; rice bran (RB), rice husk (RH), and rice germ (RG) were compared for their use as reducing agents in synthesis of silver nanoparticles (AgNPs). AgNPs from those three different parts of rice, RB-AgNPs, RH-AgNPs, and RG-AgNPs, respectively showed different reducing activity, which the highest capacity was RB. RG-AgNPs and RB-AgNPs showed the maximum absorption of AgNPs at 440 nm whereas that of RH-AgNPs was at 480 nm. FTIR spectra of all AgNPs indicated the presence of different functional groups from rice attached to the nanoparticles and these groups prevented the particle agglomeration. Size analysis using dynamic light scattering revealed that RB-AgNPs was the smallest particles (346.4 ± 36.8 nm) and possessed the highest negative zeta potential. Antimicrobial test showed that the AgNPs obtained from green synthesis mediated by rice extracts have great antimicrobial activity against Streptococcus mutans, the severe oral pathogenic bacteria causing dental caries. These results suggest that aqueous extracts of RB, RH, and RG have potential to be used as reducing agents in synthesis of silver nanoparticles.

Silver nanoparticles (AgNPs) receive increase interest in application for many fields (1) due to their efficiency in antibacterial (2), antifungal (3), antiviral (4), anticancer (5), and antioxidant activities (6). Synthesis of AgNPs can be generally performed by reacting silver salts with certain reducing agents from natural such as plant extracts (7) or chemically synthesized agents (8). The reducing agents from natural resources have gain increasing interest since there are less hazardous waste than those from chemical synthesis. Polysaccharides are one of the natural interesting groups that some of them, e.g. starch, dextran, and cellulose were used as a reducing agent for synthesis of metal nanoparticles. For example, our group previously reported the use of starch derivatives from rice for synthesis of AgNPs (9). Bankura et al. reported the use of dextran to synthesize gold nanoparticles (10). For cellulose, there are some reports on using cellulose derivatives such as methylcellulose and carboxymethyl cellulose to synthesize AgNPs (11-13). However, there is still less report on factors affecting the obtained AgNPs synthesized by using cellulose derivatives as a reducing agent as well as the comparison of reducing efficiency among many types of cellulose derivatives.Cellulose is an organic polysaccharide consisting SummaryThe aim of this study was to synthesize silver nanoparticles (AgNPs) by using cellulose derivatives as a reducing agent. Methyl cellulose (MC), hydroxy ethylcellulose (HEC), and hydroxypropyl methylcellulose (HPMC) were compared for their reducing property. HPMC presented the highest reducing power, with equilibrium concentration (EC) of 84.6 ± 4.5 µmol Fe 2+ /g, followed by MC and HEC, with the EC of 62.3 ± 1.4, and 38.1 ± 3.2 µmol Fe 2+ /g, respectively. Using these cellulose derivatives as a reducing agent and silver nitrate as a precursor in fabrication of silver nanoparticles (AgNPs), three cellulose-AgNPs, HEC-AgNPs, MC-AgNPs, and HPMC-AgNPs, were obtained. The cellulose-AgNPs showed different maximum absorptions confirming AgNPs spectra at 415, 425, and 418 nm, respectively. Reaction parameters such as pH, temperature, and period of reaction affected intensity of the maximum absorptions and size of AgNPs. Using 0.3% cellulose solution at pH 9 and reaction at 70°C for 90 min, the particle size of MC-AgNPs, HEC-AgNPs, and HPMC-AgNPs was 97.7 ± 2.4, 165.6 ± 10.6, and 51.8 ± 1.6 nm, respectively. AgNPs obtained from different cellulose derivatives and various preparation parameters possess different inhibition potential against Escherichia coli and Staphylococcus aureus. The cellulose-AgNPs have higher effective against E. coli than S. aureus. HPMC-AgNPs showed significantly higher antibacterial activity than MC-AgNPs and HEC-AgNPs, respectively.These results suggest that the type of cellulose derivatives and the reaction parameters of the synthesis such as pH, temperature, and reaction period play an important role to the yield and physicochemical property of the obtained AgNPs.

Nowadays, silver nanoparticles (AgNPs) are of high interest due to their particular properties and wide applications. AgNPs are used to inhibit many pathogenic including bacteria such as Staphylococcus aureus, Escherichia coli, Salmonella enteritidis, and Pseudomonas aeruginosa (1-3) and fungi like Aspergillus and Candida spp. (4,5). AgNPs can be synthesized by redox reaction of silver salt as a precursor and a reducing agent from synthetic chemicals. Recently, the ecofriendly process of AgNPs production was developed using reducing agents from natural sources like plants (5), algae (6), and microorganisms (7). Caesalpinia sappan is a plant belongs to familily Leguminosae. It is wildly distributed and cultivated in Southeast Asia, Africa and the America (8). The wood of C. sappan contains several phytochemicals in alkaloids, phenolics, flavonoids, and glycosides (9). The major active compound of C. sappan is brazilin and brazilein, an oxidized from of brazilin (10,11). Many biological activities from different parts of C. sappan have been reported such as antioxidant activity from heart woods (12), antihelmintic property from leaves (13), and antimicrobial activity from barks (14). The aim of this study was to synthesize AgNPs Summary The aim of this study was to investigate the antioxidant activity of Caesalpinia sappan aqueous extract (CE) and its potential on synthesis of silver nanoparticles (AgNPs). The antioxidant activity of CE was investigated using ferric reducing antioxidant power (FRAP) assay and two radical scavenging methods using 2,20-azinobis-(3-ethylbenzothiazoline-6sulfonic acid) diammonium salt (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) as free radicals. Silver nitrate (AgNO 3) was used as precursor for the synthesis of AgNPs. Effects of AgNO 3 concentration, reaction temperature, and duration of reaction were investigated. The obtained AgNPs was characterized using UV-Vis and photon correlation spectrophotometers. The antimicrobial activity of AgNPs was studied by means of diffusion method. The results from FRAP demonstrated that CE had high reducing property of 78.7 ± 2.4 mM Fe 2+ /mg. The trolox equivalent antioxidant capacity of CE determined by ABTS was 64.8 ± 4.2 µM/mg. The concentration of CE that can inhibit 50% of DPPH radicals (IC 50) was 51.2 ± 3.2 µM. These results indicated that CE possesses strong antioxidant and reducing activities. The present study also showed that CE can act as reducing agent to produce AgNPs. The concentration of AgNO 3 , reaction temperature, and reaction time play an important role on the particles size and zeta potential of the obtained AgNPs. The antimicrobial activity of the AgNPs against Escherichia coli, Candida albicans, and Streptococcus mutants was stronger than against Staphylococcus aureus.

No abstract

In the present study, three different rice varieties; Jasmine (JM), Niaw Koko-6 (NKK), and Saohai (SH) were determined for reducing power using ferric reducing antioxidant power (FRAP) assay. SH showed the highest reducing property followed by JM and NKK, respectively. All modified rice samples were used to fabricate silver nanoparticles (AgNPs) by reducing silver nitrate (AgNO 3 ) to metallic Ag. The obtained AgNPs from JM, NKK, and SH namely JM-AgNPs, NKK-AgNPs, and SH-AgNPs, respectively, showed maximum absorption at 410, 408, and 409 nm, respectively, which confirmed the spectra of AgNPs. Reaction parameters such as AgNO 3 and modified rice concentration as well as the reaction period were investigated. It was found that increasing of these parameters gave better AgNPs until the concentration of modified rice and AgNO 3 reached to 0.3% and 10 mM, respectively and the reaction period reached to 60 min, the most suitable AgNPs were obtained. Among the three rice varieties, SH showed the most potential for synthesis of AgNPs. SH-AgNPs showed the smallest size of 80.4 ± 2.8 nm and the highest zeta potential of -45.9 ± 1.4 mV. The AgNPs obtained from all three rice varieties showed effective against Escherichia coli than Staphylococcus aureus and SH-AgNPs showed significantly higher antibacterial activity than JM-AgNPs and NKK-AgNPs.