title: Immobilization free electrochemical biosensor for folate receptor in cancer cells based on terminal protection.
abstract: The determination of folate receptor (FR) that over expressed in vast quantity of cancerous cells frequently is significant for the clinical diagnosis and treatment of cancers. Many DNA-based electrochemical biosensors have been developed for FR detection with high selectivity and sensitivity, but most of them need complicated immobilization of DNA on the electrode surface firstly, which is tedious and therefore results in the poor reproducibility. In this study, a simple, sensitive, and selective electrochemical FR biosensor in cancer cells has been proposed, which combines the advantages of the convenient immobilization-free homogeneous indium tin oxide (ITO)-based electrochemical detection strategy and the high selectivity of the terminal protection of small molecule linked DNA. The small molecule of folic acid (FA) and an electroactive molecule of ferrocence (Fc) were tethered to 3'- and 5'-end of an arbitrary single-stranded DNA (ssDNA), respectively, forming the FA-ssDNA-Fc complex. In the absence of the target FR, the FA-ssDNA-Fc was degraded by exonuclease I (Exo I) from 3'-end and produced a free Fc, diffusing freely to the ITO electrode surface and resulting in strong electrochemical signal. When the target FR was present, the FA-ssDNA-Fc was bound to FR through specific interaction with FA anchored at the 3'-end, effectively protecting the ssDNA strand from hydrolysis by Exo I. The FR-FA-ssDNA-Fc could not diffuse easily to the negatively charged ITO electrode surface due to the electrostatic repulsion between the DNA strand and the negatively charged ITO electrode, so electrochemical signal reduced. The decreased electrochemical signal has a linear relationship with the logarithm of FR concentration in range of 10fM to 10nM with a detection limit of 3.8fM (S/N=3). The proposed biosensor has been applied to detect FR in HeLa cancer cells, and the decreased electrochemical signal has a linear relationship with the logarithm of cell concentration ranging from 100-10000cell/mL. Compared with the traditional heterogeneous electrochemical FR biosensors, the proposed biosensor owns the merits of the simplicity and high specificity, presenting the great potential application in the area of early diagnosis of cancers.
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China; Department of Chemistry and Environment Science, Fujian Province University Key Laboratory of Analytical Science, Minnan Normal University, Zhangzhou 363000, China.
authors.forename: Jiancong
authors.initials: J
authors.lastname: Ni
authors.affiliation: Department of Chemistry and Environment Science, Fujian Province University Key Laboratory of Analytical Science, Minnan Normal University, Zhangzhou 363000, China. Electronic address: axiang236@126.com.
authors.forename: Qingxiang
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Yang
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Zhao
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Longhua
authors.initials: L
authors.lastname: Guo
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Qiu
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China. Electronic address: zylin@fzu.edu.cn.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Ministry of Education Key Laboratory of Analysis and Detection for Food Safety, Fujian Provincial Key Laboratory of Analysis and Detection for Food Safety, Department of Chemistry, Fuzhou University, Fuzhou 350116, China.
authors.forename: Huang-Hao
authors.initials: HH
authors.lastname: Yang
mesh_terms: D015374:Biosensing Techniques / Q000379:methods; D004277:DNA, Single-Stranded / Q000737:chemistry*; D055664:Electrochemical Techniques / Q000379:methods*; D004566:Electrodes; D005090:Exodeoxyribonucleases / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D058973:Folate Receptors, GPI-Anchored / Q000032:analysis*; D005492:Folic Acid / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D057230:Limit of Detection; D000075163:Metallocenes; D009369:Neoplasms / Q000473:pathology*; D015203:Reproducibility of Results; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D004277:DNA, Single-Stranded; D005296:Ferrous Compounds; D058973:Folate Receptors, GPI-Anchored; D000075163:Metallocenes; D017971:Tin Compounds; C109984:indium tin oxide; D005492:Folic Acid; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; C004998:ferrocene
keywords: Cancer cells; Electrochemical biosensor; Folate receptor; Immobilization free; Terminal protection