Studies On Biosensor Of Folic Acid Based On Gold Nanoparticles

Gold nanoparticles(Au NPs) have been becoming an important material for sensors due to its unique physical, chemical, optical and catalytic properties. Au NPs can be synthesized in a straightforward manner.They showed highly stability and unique optoelectronic properties. Au NPs possess high surface-to-volume ratio with excellent biocompatibility when combine with ligands. Recently, Au NPs, as a sensory element have been used to detect metal ions, small molecules, proteins, nucleic acid,malignant cells etc.Folic acid(FA),(N-[ p-{[(2-amino-4-hydroxy-6-pteridinyl)methyl]amino}benzoyl]-l-glutamic acid) is a water-soluble B-vitamin that occurs naturally in a wide variety of foods, such as broccoli, cabbage, cauliflower, fruit and nuts. Folate receptor is over-expressed in many tumor cells. Thus, folic acid is applied to the biosensor as a tumor maker. The deficiency of FA in the diet can lead to megaloblastic anemia,cancer, Alzheimer’ s disease, cardiovascular disease.This paper developed three kinds of folic acid biosensors based on the gold nanoparticles. Details are presented as follows:1. Gold nanoparticles modified with chitosan folic acid for the detection of breast cancers MCF-7 cellsA well-designed folic acid sensor for breast cancers detection has been developed. The gold nanoparticles were deposited on the surface of glass carbon eletrode. Then a mixture layer consisted of chitosan and folic acid was coated on the surface of gold nanoparticles. The biosensor showed good elelctrochemical response to FA, and the current response of the biosensor increased linearly with the concentration of breast cancer MCF-7 from 5.0×103 cells/m L to 1.2×105 cells/m L (with a relative coefficient of 0.9935). When the concentration of breast cancers cells was 40 mg/m L, cell mortality was 18 %. This folic acid sensor is easy to prepare and could be applied in vivo effectively.2. Based on gold nanoparticles SERS signal for the detection of cervical cancers He La cellsFolate receptor(FR) is a kind of tumor-associated antigen, which is over-expressed in He La cells with a high affinity to folic acid. Gold nanoparticles were used as SERS substrate and 4-mercaptobenzoic acid as the Raman beacon. The gold nanoparticles were encapsulated by a layer of silicon dioxide with an appropriate thickness to prevent the toxic effects of nanoparticles to cells. The cervical cancer He La and human lung adenocarcinoma A 549 could be tested by the surface Raman enhanced scattering. He La cells has strong Raman signal, and A 549 did not show obvious signal. This analysis technique is promising to be a new method for the detection of cancer cells based on folic acid biosensor, and to be applied directly to early cervical cancer diagnosis in vitro.3.Folic acid sensors based on gold nanoparticles/multi-walled carbon nanotubeThe multi-walled carbon nanotubes were mixed with gold nanoparticles, then the mixture was added to the surface of glassy carbon electrode. The behavior of the biosensor was investigated by cyclic voltammetry(CV), impedance spectrum(EIS)and differential pulse voltammetry(DPV) for the detection of folic acid. Under the optimum experiment conditions,the current response of the sensor increased linearly with the concentration of folic acid from 2.0×10-6 M to 2.0×10-4 M with a relative coefficient of 0.9967 and the detection limit was 2.9 cells ml-1(S/N=3).