Fluorescent Detection Of Interaction Between Semiconducting Carbon Nanotubes And Fibrinogen

Label-free fluorescent probes and biosensors based on semiconducting single-wall carbon nanotubes,fluorescence characteristics of which are sensitive to external environment,have been widely used in the field of biomedicine.However,single-wall carbon nanotubes currently used are almost mixed structure,which include semiconducting single-wall carbon nanotubes with fluorescent property and metallic single-wall carbon nanotubes which quench fluorescence.In addition,whether energy transfer between different chiral carbon nanotubes will influence normal fluorescent detection of biomolecules has not been verified.Moreover,excitation wavelengths of carbon nanotubes with different chirality are not uniform,higher signal-to-noise ratio of fluorescence response can be obtained only by the corresponding resonance excitation,and then properly describe degree of interaction between carbon nanotubes and biomolecules.Due to enantiomers of single-chiral single-wall carbon nanotubes,their effects should also be considered when interacting with chiral biomacromolecules.Recently,one kind of amphiphilic phospholipid-polyethylene glycols(DPPEmPEG5000)not only disperses single wall carbon nanotubes through simple noncovalent modification,but also constructs corona phase site to specifically recognize protein.Hence,we will exploit it to construct fluorescent probes based on carbon nanotubes to study the effect of carbon nanotube structure on the interaction of biomacromolecules,fibrinogen,in detail.In this paper,we obtain enrichment of semiconducting carbon nanotubes and enantiomers of single-chiral(6,5)by gel selective adsorption.Dispersant on the sidewall of carbon nanotube is replaced by SDS using ultrafiltration replacement method firstly,and then replaced with the biocompatible DPPE-mPEG5000.After that,with the help of data from fluorescence response of carbon nanotubes to fibrinogen with different concentrations under resonance excitation condition,the degree of interaction is analyzed by Hill model.By detecting secondary structure of fibrinogen and fluorescence response of carbon nanotubes in the mixed solution of fibrinogen and carbon nanotubes,we confirm that carbon nanotubes obtained by the replacement process possess good biocompatibility and removal of surfactants has met the requirements for stable fluorescence detection.By studying the interaction of semiconducting single-wall carbon nanotubes obtained using different concentrations of DPPE-mPGE5000 with fibrinogen,we found that:1.As the concentration of DPPE-mPGE5000 increases during the replacement process,initial fluorescence intensity of various chiral carbon nanotubes increases firstly and then decreases,but parameter k of interaction between carbon nanotubes and fibrinogen is not linear related to that concentration.2.Diameter of carbon nanotubes has a more significant effect on the interaction with fibrinogen,compare to other structure parameters,such as chiral angle,minimum C-C bond curvature,and semiconducting type.As the diameter decreases,the binding ability of carbon nanotubes after replacement to fibrinogen is enhanced and degree of fluorescence quenching increases.And fluorescence response of(6,5)with small diameter to fibrinogen is more stable.Next,in order to exclude influence from inconsistent ratio of different chiral carbon nanotubes and energy transfer between carbon nanotubes,we studied interaction between enriched enantiomers of single-chiral single-wall carbon nanotubes(6,5)coated with DPPE-mPEG5000 and fibrinogen and found that:1.In terms of fluorescence response,there is always no statistically significant difference in the binding of left and right-handed(6,5)to fibrinogen by adjusting concentration of DPPE-mPEG5000 during the replacement process.2.Further decrease of DPPE-mPEG5000(0.05 mg/ml)concentration during replacement process,the binding ability of single-wall carbon nanotubes to fibrinogen is significantly weakened,collaborative effect is significantly increased,and degree of fluorescence quenching reduces significantly.Not only it shows exposed surface of carbon nanotubes appears,but also indicates that the decrease of the fluorescence intensity of the carbon nanotubes is caused by conformational transformation of DPPEmPEG5000 on the sidewall of carbon nanotubes rather than direct contact between fibrinogen and carbon nanotubes.3.Single-chiral(6,5)carbon nanotubes exhibit a lower degree of maximum fluorescence quenching than(6,5)in semiconducting carbon nanotubes,but the former have stronger binding ability to fibrinogen than the latter.All in all,we think that fluorescence response of carbon nanotubes wrapped by DPPE-mPEG5000 to fibrinogen is caused by combination of fibrinogen and recognition site constructed by DPPE-mPEG5000,and fibrinogen changes the conformation of DPPE-mPEG5000 on the surface of carbon nanotubes and then leads to decrease of fluorescence efficiency of carbon nanotubes.The carbon nanotubes obtained by selecting suitable concentration(0.25 mg/ml)of DPPE-mPEG5000 during replacement process can not only maintain excellent ability to recognize fibrinogen,but also obtain better signal-to-noise ratio.After eliminating influence of enantiomers on recognition ability,fluorescence response of single-chiral(6,5)carbon nanotubes under resonance excitation reflect binding ability to fibrinogen more accurately.On this basis,it is possible to further improve the modification conditions and design a biological fluorescent probe that is more in line with human environment.