first , research in the field of natural organic nanoparticles is new to material science .
although natural nanostructures with biological functions have been found for many years , natural organic nanoparticles have not been investigated for material properties such as mechanical and optical properties until recent years .
these nanoparticles formed of organic molecules and polymers offer variable optical properties due to the abundant alternative components .
however , in the case of biological applications , organic nanoparticles formed in nature are also a promising alternative due to their compatibility and non - toxicity .
natural nanoparticles can be used as the functional materials just as the artificial nanoparticles . optical absorption and light scattering
the ingredients of modern sunscreens usually contain organic compounds , inorganic nanoparticles   and organic nanoparticles .
the inorganic nanoparticles ( such as zno and tio2 ) and organic nanoparticles can reflect , absorb and scatter the solar light .
though inorganic nanoparticles have been widely used in cosmetic products , there are still concerns about the toxicity of these inorganic materials .
tio2 has been reported to induce dna   and rna   damage through the process of chemical oxidation . considering these situations ,
if nature - derived harmless organic nanoparticles have strong ultraviolet absorption , they will be a potential promising alternative for sunscreen . in this paper , we reported the optical absorption and light scattering of ivy nanoparticles .
the advantages of these nanoparticles in their application to sunscreen compared to inorganic nanoparticles were also demonstrated .
fresh - grown rootlets of english ivy were collected around the university of tennessee , knoxville campus , before attaching themselves to solid surfaces .
the collected rootlets were meshed using tweezers in 5-ml clean tube containing 500l of 20-nm - filtered water after washing them three times with ddh2o .
the solution was then centrifuged at 3000 rpm for 5 min , and the supernatant was collected .
two - thirds of the solution was dialyzed overnight at 4 degrees with ddh2o through a cellulose membrane ( sigma  aldrich , d9277 ) allowing free pass of chemicals less than 12,500 daltons .
size exclusion chromatography and high - performance liquid chromatography ( sec  hplc ) was used to isolate the nanoparticles from the solution .
the varian hplc system consists of three components including varian prostar 210 , the varian prostar 335 detector and the varian prostar 430 autosampler .
next , 200 l of dialysis solution was loaded to the column ( phenomenex   biosep - sec - s3000 column with an attached security guard   cartridge system ) . the running speed of the mobile phase was set to 0.5 ml / min , and the back pressure of the column was 580 psi .
these samples we investigated in this study were named sec-1 , sec-2 and sec-3 with the time sequence .
the non - dialysis solutions were also prepared and named nd220 and nd20 , respectively .
the morphologies of the ivy nanoparticles were observed by agilent 5500 atomic force microscope ( agilent technologies , santa clara , ca ) .
the instrument was operated at room temperature ( 20c ) using picoview in ac mode , which means little or no contact between the tip and the sample .
dynamic light scattering ( dls ) measurements were performed by a brookhaven instruments bi-200sm goniometer equipped with a pci bi-9000at digital correlator .
the detector is located at the scattering angle of 90. the ultraviolet and visible ( uv  vis ) extinction ( absorption and scattering ) spectra were measured by the thermo scientific evolution 600 uv - visible spectrophotometers .
, size distributions of the ivy nanoparticles were observed in the samples of sec-1 , sec-2 , d220d1 and nd220 by dynamic light scattering ( dls ) measurement .
this effect is believed to be due to the low concentration of ivy nanoparticles in sec-3 .
the sizes of nanoparticles display the large ranges from tens of nanometers to several hundred nanoparticles .
the average diameters of particles are 117.4 nm for sec-1 , 131.6 nm for sec-2 , 97.8 nm for d220d1 and 112.3 nm for nd220 .
it is worth to note , in principle , dls gives the hydrodynamic sizes of the particles .
the hydrodynamic sizes are usually greater than the sizes of dry particles obtained by afm .
large particles scatter a significant amount of light so that the diameters given by dls intensity distributions will be greater than that obtained by afm even if there are only a few large particles   fig .
the morphologies of ivy nanoparticles observed by afm size distributions of ivy nanoparticles in water ( sec-1 and d220d1 ) obtained by dynamic light scattering the extinction spectra of samples from the sec technology and the filtration are shown in fig .
the extinction spectra of ivy nanoparticles using the filtration method are obtained by subtracting the extinction spectra of samples filtered using 20-nm filters from those filtered by 220-nm filters .
for example , the curve in fig . 3b with the symbol of high concentration denotes the difference between the extinction spectra found in d220d1 and d20d1 .
the spectrum characteristics of those samples from the sec technology and the filtration are approximately consistent . these phenomena including the dls results mean that the sec and the filtration are the effective direct and indirect methods to investigate the optical properties of ivy nanoparticles .
these nanoparticles display strong ultraviolet and weak visible light extinction and , interestingly , a sharp transition edge from the ultraviolet to the visible range .
a significant extinction band and a shoulder can be found around the wavelengths of 280 nm and 325 nm for all the samples , respectively .
vis extinction spectra of ivy nanoparticles in the samples prepared by a size exclusion chromatography technology and b the filtration .
high concentration ( low concentration , non - dialysis ) represents the difference between the extinction spectra found in d220d1 ( d220d2 , nd220 ) and d20d1 ( d20d2 , nd20 ) to illustrate the content of the solution , the original spectra are shown before subtraction in fig .
4 . the extinction band and the shoulder are at the same positions not only for the samples filtered through the 220-nm filters but also the ones filtered through the 20-nm filters .
this similarity implies that the components in the solutions are similar to that of the ivy nanoparticles .
in addition , the non - dialysis samples show differences when compared to the dialysis samples in the original absorption spectra in fig .
4 . this may be due to the dialysis process in which some protein or other molecules less than 12,500 daltons are filtered out .
the absorption peak at the wavelength of 280 nm is the characteristic for many proteins . in general , three of the amino acid side chains ( trp , tyr and phe ) contribute significantly to the uv absorption of a protein at 280 nm .
those amino acids are believed to form ivy nanoparticles , but the actual types of proteins and amino acids are still under investigation .
furthermore , the concentration of ivy nanoparticles in the sample of high concentration ( d220d1-d20d1 ) was measured to be 4.92 g / ml by the bradford protein assay .
original extinction spectra of the filtered samples scattering ( just as the tyndall effects shown in dls experiments ) also makes considerable contribution to the total extinction besides the absorption .
herein , we simulated extinction behaviors of the ivy nanoparticles by the mie scattering theory with the help of the software mietab 8.38 .
while the refractive index of most organic compounds is between 1.3 and 1.73 , the refractive index of ivy nanoparticle was set to 1.5 .
the refractive index of water from 280 nm to 400 nm was from the reported data .
the fitting curve of the total extinction , scattering and absorption curves are shown in fig .
the scattering effect is found to contribute to the extinction , although this contribution is much smaller than that of the absorption .
3b the characteristics of extinction spectra of ivy nanoparticle make a great advantage in the sunscreen application for blocking the ultraviolet light and maintaining the high visible transparence .
ivy nanoparticles can use their optical absorption and scattering properties to eliminate the ultraviolet light , just as inorganic nanoparticles such as zno and tio2 do in sunscreen . in order to illustrate the relative ultraviolet 
visible extinction characteristics , solutions of zno nanoparticles ( nanoamor , 99.9% , 90200 nm ) and tio2 nanoparticles ( nanoamor , rutile , 99% , 50 nm ) were adjusted to be the same extinction value as sec-2 at 280 nm . this wavelength is the beginning of uv - b ( 280320 nm ) .
sunscreens protect from both uv - b and uv - a ( 320400 nm ) irradiation . in fig .
6a , the ivy nanoparticles display a sharper edge from the ultraviolet range to the visible range .
herein , the concentrations of tio2 and zno suspensions are 23 g / ml and 100 g / ml , respectively .
after this , the extinction spectra of the above tio2 and zno suspensions were roughly converted to the spectra with the concentration of 4.92 g / ml , as shown in fig .
6b . the ivy nanoparticles ( high concentration ) exhibit a much stronger ultraviolet absorption and sharper decrease near the visible range .
due to the non - toxicity and strong extinction property , ivy nanoparticles are a promising material for sunscreen application .
comparison of the uv  vis extinction spectra of tio2 , zno nanoparticles and ivy nanoparticles . a the relative uv  vis extinction characteristics with the same extinction value at 280 nm .
b the extinction behaviors at the same concentration ( 4.92 g / ml ) natural or biological nanoparticles have not been investigated in detail for their material properties . in this study , we investigate these type nanoparticles as the functional materials just like usual inorganic and organic nanoparticles .
nanoparticles from the original tiny ones to the mature ones all exit in the rootlets of ivy .
the sec technology isolated the nanoparticles from the mixed solutions including molecules , but it did not give us uniform size of nanoparticles .
recently , in order to increase refractive index of organic polymers , surface modification methods , such as deep uv modification and ion - beam implantation , have been reported .
if similar modifications are applied to ivy nanoparticles , the refractive index mismatch between ivy nanoparticles and the medium will become larger .
this effect can increase the light scattering of ivy nanoparticles and , furthermore , benefit the extinction .
in conclusion , ivy nanoparticles have been isolated by the sec technology and the filtration methods . optical absorption and scattering properties of these nanoparticles
the extinction spectra of the ivy nanoparticles display strong ultraviolet and weak visible extinction with a sharp transition edge . compared to inorganic nanoparticles , ivy nanoparticles can be used in ultraviolet protection due to their optical properties and harmless nature .
this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
 though much research has been conducted for nanoparticles , naturally occurring nanoparticles have not yet been well explored for their diverse properties and potential applications . this paper reports the optical absorption and scattering properties of nanoparticles secreted by english ivy . 
 both experimental and theoretical studies have been conducted . 
 strong ultraviolet extinction and excellent visible transparency are observed , compared to the inorganic tio2 and zno nanoparticles at similar concentrations . 
 the contributions of absorption and scattering to the total extinction are quantified by simulation of the mie scattering theory . 
Introduction
Experiments
Results and Discussion
Conclusions
Acknowledgments
Open Access