Biosynthesis and characterization of titanium dioxide nanoparticles using pithecellobium dulce and lagenaria siceraria aqueous leaf extract and screening their free radical scavenging and antibacterial properties

. The recent development and implementation of new technologies have led to new era, the nano-revolution which unfolds role of plants in bio and green synthesis of nanoparticles which seem to have drawn quite an unequivocal attention with a view of synthesizing stable nanoparticles. In this present work, we have compared titanium dioxide nanocrystals synthesized by both chemical method and biological method from Titanium tetra isopropoxide as precursor. The biological method was performed by using the aqueous plant extract of Pithecellobium dulce and Lagenaria siceraria. The synthesized nanocrystals were characterized by FTIR Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Xray (EDAX), Transmission Electron Microscope (TEM) and X-ray diffraction (XRD) techniques and also Antioxidant assay and antimicrobial test were performed to evaluate its biological behaviour. The nanocrystals synthesized by biological method were found to have higher antioxidant potential, antimicrobial activity than chemically synthesized.


INTRODUCTION
Biological synthesis of nanoparticles by plant extract is at present under exploitation for the reason that to develop environmentally benign nanoparticles synthesis to avoid adverse effects in biomedical applications (M. Sundrarajan et al2011). The manipulation of matter on an atomic, molecular, and supramolecular scale. The earliest, widespread description of nanotechnology, Nanoparticles are usually ≤100 nm in each spatial dimension or less have attracted great attention due to their unusual and fascinating properties, Nanoparticle research is currently an area of intense scientific interest due to a wide variety of potential applications in biomedical, optical and electronic fields and applications advantageous over their bulk counterparts [M. C. Daniel et al, 2004]. Nanoparticles are classified primarily into two types, viz organic and inorganic nanoparticles. The nanoparticles of carbon are called the organic nanoparticles. Magnetic nanoparticles, noble metal nanoparticles (platinum, gold and silver) and semiconductor nanoparticles (titanium dioxide, zinc oxide and zinc sulfide) are classified as inorganic nanoparticles (Kathiresan et al, 2013).
Titanium dioxide (TiO 2 ), an important semiconductor nanoparticle has been interesting attention for its wide range of applications, such as electronics, optics, optoelectronics, transparent, UV-light emitters, piezoelectric devices, chemical sensors, spintronics. Further, TiO 2 NPs exhibit size and shape-dependent properties which are of interest for applications ranging from biosensing and catalysts to optics, antimicrobial activity, computer transistors, electrometers, chemical sensors, and wireless electronic logic and memory schemes. These particles also have many applications in different fields such as medical imaging, nanocomposites, filters, drug delivery, and hyperthermia of tumors (D. Bhattacharya et al, 2005; D. Goodsell, 2004; R. Paull et al, 2003; O. V. Salata, 2004). Nanoparticles are usually 0.1 to 1000 nm in each spatial dimension and are commonly synthesized using two strategies: top down and bottom up. In top-down approach, the bulk materials are gradually broken down to nanosized materials, whereas in bottom-up approach, atoms or molecules are assembled to molecular structures in nanometer range. Bottom-up approach is commonly used for chemical and biological synthesis of nanoparticles, by chemical methods leads to the presence of some toxic chemical species adsorbed on the surface that may have adverse effects in medical applications. Due to the obvious disadvantages of the chemical reduction method, a biological synthesis of nanomaterials is an important aspect of nanotechnology. There is a growing need to develop simple, low-cost, eco-friendly and size control approaches for the synthesis of metal nanoparticles. Biological route synthesis of nanoparticles has received much focused attention from researchers in order to elucidate the mechanism of synthesis. To circumvent this many biological systems like bacteria [Kumar CG et al, 2011], fungi [Rodriques AG et al, 2012], yeast, cyanobacteria, actinomycetes and plants have been used. But the best one appears to be the use of plants.
However, review of literature revealed that the synthesis of metal oxides and semiconductors nanoparticles using plant has been explored in number of few literatures [Mahdavi M, 2013], which aroused our interest in the present study the synthesis of TiO 2 nanoparticles by utilizing the aqueous leaf extract of P. dulce and Lagenaria siceraria. Pithecellobium dulce (P. dulce) Benth (Fabaceae) is a small to medium sized, evergreen, spiny tree, up to 18 m height, native of tropical America and cultivated throughout the plains of India and in the Andamans. It is known as 'Kodukkapuli' in Tamil. The bark of the plant is reported to be used as astringent in dysentery, febrifuge and it is also used in dermatitis and eye inflammation. In traditional medicine practice, the leaves of P. dulce are used for the treatment to fearache, leprosy, pepticulcer, toothache, venereal diseases and also act as emollient, anodyne, larvicidic and abortifacient, and antidiabetic properties in folk medicine. The presences of steroids, saponins, lipids, phospholipids, glycosides, glycoli. And the Lagenaria siceraria leaf, Bottle gourd (Lagenaria siceraria (Mol.) standley, family Cucurbitaceae) commonly called as Dudhi or Ghiya is widely cultivated in the tropical and subtropical regions of the world, Lagenaria siceraria, which has diuretic and anti-swelling effects, is used as food. A decoction of Lagenaria siceraria is employed in the treatment of anasarca, ascites and beriberi [Deshpande et al., 2008].So far, there is no report on the synthesis of TiO 2 by utilizing the aqueous leaf extract of Pithecellobium dulce and Lagenaria siceraria. Hence, the present study involves the synthesis and characterization of Pithecellobium dulce and leaf mediated TiO 2 and evaluating the anti-bacterial effect of biosynthesized TiO 2 in comparison to chemically synthesized TiO 2 and plant extract against human pathogens such as gram-positive and gram-negative bacteria.

Materials
Titanium tetraisopropoxide [Ti (OCH (CH 3 ) 2 ) 4 ], Isopropanol (C 3 H 7 OH), Acetic acid (CH 3 COOH) and ethanol were purchased from Sigma Aldrich, India. All the chemicals were used without any further purification. Nutrient media used for antibacterial activity were purchased from Hi-Media, Mumbai, India. All aqueous solutions were prepared using de-ionized water. All glass wares were cleaned with chromic acid followed by thorough washing with de-ionized water and then acetone for prior use.
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Preparation of aqueous leaf extract
Lagenaria siceraria and Pithecellobium dulce leaf were collected from rural areas of Chidambaram, Tamil Nadu, India. Leafs were washed thoroughly with tap water and dried in the shade. Dried leafs were cut into small pieces and ground coarsely using pulverizer. Soxhlet extraction was then performed to obtain the crude aqueous extract which is stored in the refrigerator for further use.

Synthesis of titanium dioxide nanocrystals By chemical method
TiO₂ nanocrystals were prepared by the sol gel technique. Metal precursor Titanium tetraisopropoxide (2 mL) was added to solvents Isopropanol (2 mL) and acetic acid (1 mL). It was rapidly stirred at room temperature and distilled water was added drop wise to obtain sol gel transformation. It was then air dried and calcined at 450°C for 30 minutes to obtain nanocrystalline TiO₂.

Biosynthesis of TiO 2 nanoparticles
For the synthesis of titanium dioxide nanoparticles, the Erlenmeyer flask containing 0.4M of titanium tetraisoproxide in ethanolic leaf extract was reacted under stirring at 50°C. After four hours of continuous stirring, the formed titanium dioxide nanoparticles was acquired by centrifugation at 10000 rpm for 15 minutes. Then the centrifuged particles were washed with ethanol and again subjected to centrifugation at 5000rpm for 10 minutes. Separated titanium dioxide nanoparticles were dried and grinded to calcinate at 500°C in muffle furnace for about 3 hours. The calcined titanium dioxide nanopowder was used for further analytical techniques. from Pan Analytical instruments operated at a voltage of 40 kV and a current of 30 mA with Cu Ka radiation.Fourier transform infrared spectroscopy. FT-IR spectroscopic studies were carried out to identify the possible functional groups in the leaf extract responsible for capping leading to efficient stabilization of the TiO 2. The FT-IR spectra of powdered TiO 2 were mixed with KBr pellets and are recorded in the 4,000-400 cm -1 range on a Shimadzu FTIR-8400s

Antimicrobial activity
In the present study, in vitro antimicrobial activities were carried out by the using of diskdiffusion method [H.W. Seely et al, 1975; A. L. Barry, 1976]. This method followed the following procedure: First of all, Petri plates were prepared with 20 mL of sterile Muller Hinton Agar . Then, the 24 h prepared test cultures of inoculums were swabbed on the top of the solidified media and allowed to dry for 10 min. chemically and biosynthesized TiO 2 nanoparticles impregnated disks at the concentrations of 50 µg/mL for bacteria was placed aseptically on sensitivity plates with appropriate controls. The loaded disks were placed on the surface of the medium and left for 30 min at room temperature for compound diffusion. Negative control was prepared using respective solvent. Ciprofloxacin (5 µg/disk) was used as positive control for bacteria. All the plates were then incubated at 37 0 C. The sensitivity was recorded by measuring the clear zone of growth inhibition on agar surface around the disks in millimeter.

Free radical scavenging activity
Biosynthesized Au-NPs and S. nigrum were tested for the scavenging effect on DPPH radical according to the method of [Blois, 1958] Different concentrations (50, 100 and 150 _L) of S. nigrum and biosynthesized Au-NPs were added, in equal volume, to 0.1 mM metabolic DPPH solution. The reaction mixture was incubated for 30 min at room temperature under shaking condition and the absorbance was recorded at 517 nm. The synthetic antioxidant butyl hydroxyl toluene (BHT) was used as positive control. All determinations were performed in triplicate. The DPPH radical scavenging activity (RSA) was expressed in percentage of inhibition using the following formula.
where A sample is the absorbance of the blank control and A control is the absorbance of the test sample.
In this study we have synthesized TiO 2 nanoparticles from titanium tetraisoproxide solution using Lagenaria siceraria and Pithecellobium dulce leaf extract. The green synthesised TiO 2 nanoparticles were characterised using XRD, SEM, EDX and FTIR and investigated for antibacterial activity, in comparison with chemically synthesized TiO 2 nanoparticles.

Powder X-ray diffraction (XRD)
The XRD pattern of TiO 2 nanoparticles obtained using leaf extract of Lagenaria siceraria and Pithecellobium dulce and chemically synthesized TiO 2 nanoparticles are shown in Figure 2a  In the chemically synthesized TiO₂ also, sharp diffraction peaks emerge at 2θ angles 25.22°, 37.97°, 47.12°, 54.27 and 63.37° corresponds to Bragg's reflection from 101, 004, 200, 105 and 204 crystal planes. The result of XRD analysis confirms the presence of TiO 2 nanoparticles in the green and chemically synthesized sample. The XRD peaks of green synthesized TiO 2 nanoparticles obtained using leaf extract of Lagenaria siceraria and Pithecellobium dulce and chemically synthesized TiO 2 nanoparticles differ in the broadening and intensity. The diffraction peak of the green synthesised TiO 2 nanoparticles is slightly broadened, whereas the peak of chemically synthesized TiO 2 nanoparticles is comparatively sharp. Thus, the broadening of XRD peak of green synthesized TiO 2 nanoparticles observed in our study confirms the size reduction. The XRD peak of chemically synthesized TiO 2 nanoparticles is sharp, thus indicating that their size is still larger than the green synthesized TiO 2 nanoparticles (Naheed Ahmad et al. 2012).
The average crystalline size (L) of the TiO 2 nanoparticles can be calculated from the Debye-Scherrer formula, L = 0.89l/b cos θ where L is the crystalline size (in nm), l is the wavelength (in nm), b is the full width at half maximum intensity (FWHM-in radian), and θ is the Bragg diffraction angle . The average crystalline size of TiO 2 obtained from leaf extract of Pithecellobium dulce , Lagenaria siceraria and chemically synthesized was figured out to be about 7.5 nm, 8.6nm and 18.5nm. As can be understood, these values are very close to the TEM value.  shows the aryl substituted C=C stretching of Pithecellobium dulce and Lagenaria siceraria leaf extract . The intense peak between 823 ,815 and 541, 530 cm -1 describes the Ti-O stretching bands of Pithecellobium dulce and Lagenaria siceraria leaf extract synthesized TiO 2 nonmaterial. At the same time chemically synthesized TiO 2 nanoparticles a broad absorption peak around 3433cm -1 is due to the stretching vibration of -OH groups on the TiO 2 surface. The broad band from 511 and 750 cm −1 were ascribed to the strong stretching vibrations of Ti-O-Ti bonds. In IR study, the phytochemicals present in the crude extract of the flower may interact with the surface of the TiO 2 nanoparticles, thus forming a cap. Phenol and amide capped nanoparticles were reported to possess significantly higher biomedical activities than uncapped nanoparticles. Therefore, the green synthesized TiO 2 nanoparticles may possess potential biomedical benefits than uncapped TiO 2 Nano particles (Thiyagarajan Devasena et al,2014) Fig. 4a, 4b and 4c shows the SEM images of biostabilised TiO 2 nanoparticles obtained using Pithecellobium dulce and Lagenaria siceraria leaf extract and chemical route respectively. The leaf extract mediated synthesized TiO 2 nanoparticles show monodispersity without aggregation when compared to that of chemically synthesized TiO 2 nanoparticles. \  Figure 6a, 6b and 6c , in which peaks of titanium and oxygen elements proves TiO 2 NPs prepared is essentially free from impurities. TEM Transmission electron microscopy was used to examine the morphological characteristics of the TiO 2 nanoparticles obtained using Pithecellobium dulce and Lagenaria siceraria leaf extract and chemical route respectively (Figure 5a,5b,5c). TEM images showed that sample was composed of agglomerated and isolated particles and it reveals that small particles aggregate into secondary particles because of their extremely small dimensions and high surface energy. Therefore the diameter and the size distribution of the nanoparticles are difficult to be determined precisely by

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ILCPA Volume 50 simply viewing the TEM image. The TEM image of the TiO 2 sample obtained from Pithecellobium dulce (Figure 5a) shows the presence of spherical shape with average diameter of ~ 6.3 nm. The morphology of the TiO 2 sample synthesized from Lagenaria siceraria is also spherical shape ( Figure  5b). These particles have an average diameter of about 6.6 nm. The morphology of the TiO 2 sample synthesized from chemical method spherical and hexagonal shape (Figure 5c), but the particles are greater than those found green method. These particles have an average diameter of about 14.4 nm. The TEM images of both samples show large agglomeration of the TiO 2 particles.

ANTIBACTERIAL PROPERTIES
Antibacterial activity results revealed that Pithecellobium dulce and Lagenaria siceraria leaf extract mediated synthesized TiO 2 nanoparticles acted as excellent antibacterial agents against both Gram-positive and Gram-negative bacteria when compared chemically synthesized TiO 2 nanoparticles. It is clear from the XRD and SEM results that leaf extract mediated synthesized TiO 2 nanoparticles are smaller in size compared to chemically synthesized TiO 2 nanoparticles. Figure 7 shows the zone of inhibition produced by green and chemically synthesized TiO 2 nanoparticles against both Gram-positive and Gram-negative bacterial strains. Pithecellobium dulce TiO 2 nanoparticles exhibited maximum (14 mm) bacterial growth inhibition against B. subtilis and Lagenaria siceraria TiO 2 nanoparticles exhibited maximum (11 mm) bacterial growth inhibition against B. subtilis, in the form of zone-of-inhibition studies, where diffusion of nanoparticles on nutrient agar plates inhibits growth. In contrast, chemically synthesized TiO 2 nanoparticles showed zones of inhibition of 12 mm against B. subtilis. In the case of E. coli maximum growth, inhibition zones were found to be the following; 19, 17, and 14 mm for Pithecellobium dulce, Lagenaria siceraria leaf extract, and chemical synthesized TiO 2 respectively (Figure 7 & Table 1). Similar patterns were observed in the case of P. aeruginosa, Streptococcus pyogenes and S. aureus, where the maximum zone of inhibition was exhibited by Pithecellobium dulce followed by Lagenaria siceraria and Chemical TiO 2 .. It appears that the antibacterial activity of the nanomaterials increased with increase in surface-to-volume ratio due to the decrease in size of nanoparticles.

DPPH radical scavenging activity
Free radical is unstable atoms or molecules with outer most electrons unpaired and it is highly reactive. The free radicals always strive to form stable bond, due to gaining or losing of an unpaired electron. DPPH is a stable compound and it will be reduced by accepting the hydrogen or electrons. The reducing activity of TiO 2 nanoparticles synthesized from chemical and leaf extract of Pithecellobium dulce and Lagenaria siceraria was quantified spectrophotometrically by changing the DPPH color from purple to yellow. Percent of inhibition of DPPH radical scavenging activity was presented on Table 2. The DPPH activity of the TiO 2 nanoparticles synthesized from green and chemical method were found to increase in a dose dependent manner. The DPPH radical scavenging activities were 19.02 ± 0.52, 28.76 ± 0.15 and 37.56 ± 0.60% in 50, 100 and 150 µL for chemically synthesized TiO 2 nanoparticles and 31.18 ± 0.42, 45.48 ± 0.19 and 58.20 ± 0.25% in 50, 100 and 150 µL for Lagenaria siceraria mediated synthesized TiO 2 nanoparticles whereas value obtained 40.78 ± 0.57, 53.68 ± 0.49, and 65.57 ± 0.32% in 50, 100 and 150 µL for Pithecellobium dulce mediated TiO 2 nanoparticles, respectively. The results obtained in the DPPH assay showed effective free radical inhibition by chemically and biosynthesized TiO 2 nanoparticles. The average percentage inhibition of Pithecellobium dulce mediated synthesized TiO 2 nanoparticles was showed maximum of 52% as compared to that of chemically synthesized TiO 2 nanoparticles and Lagenaria siceraria synthesized TiO 2 nanoparticles (26% and 45%) at different concentrations used in this study and the activity increased with increasing concentrations of TiO 2 nanoparticles. The radical scavenging potential is dependent on various factors such as particle size, morphology, defects etc. Thus, the antioxidant assays suggest that Pithecellobium dulce and Lagenaria siceraria mediated synthesized TiO 2 nanoparticles are good radical scavengers than chemically synthesized TiO 2 nanoparticles due to decrease particle size and increase surface area. The free radical scavenging activity is a surface reaction since only the surface comes in contact with the free radicals.

*ciprofloxacin
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CONCLUSION
In this study we have prepared TiO 2 nanoparticles by using leaf extract of Pithecellobium dulce and Lagenaria siceraria and by a chemical method. Both nanoparticles were characterized for their size, and crystallinity using XRD, FTIR and SEM. The TiO 2 nanoparticles which was capped and stabilized by phenolic and amine moieties of leaf extract was found to be lesser in size and more dispersed than the TiO 2 nanoparticles prepared by chemical method. Moreover the leaf extract prepared TiO 2 nanoparticles exhibited considerable antimicrobial activity against pathogenic bacteria, which is comparable with that of standard antibiotic and also perform antioxidant activity showed green synthesized TiO 2 nanoparticles were effective free radical inhibition than chemically synthesized TiO 2 nanoparticles. Based on these results we conclude that the leaf extract-stabilized TiO 2 nanoparticles may have potential biomedical applications when compared to chemically synthesized TiO 2 nanoparticles due to its enhanced dispersibility, stability and surface coatings.