Fabrication Of PH Sensor Based On Nano Graphene Oxide And DNA For PH Detection And Live Cell Imaging

Graphene oxide(GO)has caused increasing research interests recently,which possesses the properties of strong fluorescence quenching effect,good water solubility,low toxicity and low cost as compared with a great pitch of nano materials like carbon nanoparticles,carbon quantum dots and gold nanoparticles.And it also has great potentials in future applications including biological imaging,chemical sensing and nano-drug delivery.Because graphene oxide can both serve as a carrier for nanosensors and a fluorescent quencher for fluorescent dyes,it is very suitable for synthesing nanosensors based on graphene oxide.Moreover,compared with the organic molecular probes,nucleic acid molecular probes and fluorescent biological macromolecules,the synthesis process based on the graphene oxide nanosensor is easier and it does not require expensive equipments and complicated operation procedures.Previous studies prove that the nanosensors based on graphene oxide have high sensitivity and good specificity in the detection of metal ions.Although the number of probes synthesed basing on graphene oxide for detection of some chemicals is increasing,the synthesis of nano-sensors based on graphene oxide for pH detection and cell imaging is still in its infancy.In this paper,we propose a method for the passivation of graphene oxide surfaces with herring sperm DNA(HSD)for the preparation of GO-DNA nanosensors with high covalent eficiency.The sensor enables detection of different pH values in aqueous solutions,while the sensor can also be used to detect pH values and fluorescence imaging in cells.The folowing is the main content of this study:(1)We designed a novel fluorescent nanosensor based on graphene oxide and by utilizing the method of passivating graphene oxide surface with fish sperm DNA(HSD).In this sensor,a pH sensitive nucleic acid sequence is designed in the DNA double strands that can undergoes structural changes under acidic conditions and desorbs from the graphene oxide surface.At the same time,since the graphene oxide quenches the fluorescence of fluorescent dyes differently,the fluorescence intensity can be tuned by the pH.In this sensor,the surface of GO was passivated by HSD so that the sensor can recognize the free single-stranded and folded DNA strands efficiently,thereby expanding the range of pH detection of the sensor.Finally,a new GO-cDNA/IFO sensor that is sensitive to pH changes was synthesized,which showed highly sensitive detection both in vitro and celular experiments.(2)On the basis of above mentioned studies,we focused on designing and controling the DNA double strands in GO-DNA rationmetric pH nano-sensor.By studying different styles of DNA structure conjugation with GO,including complete complementary DNA double strands,partial complementary DNA double strands and the single strand,the highest grafting rate was achieved.In addition,we further optimized the concentration of HSD used in the passivation of GO-DNA pH nano-sensor to prepare an efficient and sensitive GO-DNA ratiometric sensor.To obtain the ratiometric nanosensor,complementary DNA duplexes labeled with double fluorescent dyes were utilized to determine the pH value of the testing solution.More importantly,the nanosensors based on GO and DNA can also achieve fluorescent imaging in cells.In summary,we have successfully synthesized pH nano-sensors based on GO and DNA by utilizing properties including the small size,strong fluorescence quenching effect and low toxicity to live cells of GO.And it can detect pH value in aqueous solutions and cells accurately.Meanwhile,in order to obtain a ratiometric pH nano-sensor based on GO and DNA,the DNA sequences with different complementary degrees modified with amino were designed to react with GO to screen out the DNA sequences with the highest covalent grafting efficiency.Further more,the concentration of HSD to passivate the surface of GO was also studied.Finally,the ratiometric pH nano-sensor based on GO and DNA was synthesized and prepared,thereby realizing different pH values in solutions and in cells.The preparation of these two nanosensors not only provide a new synthesis method for detecting pH,but also broadens the application of graphene in bioanalysing and bioimaging.