title: Fiber-Optic-Based Micro-Probe Using Hexagonal 1-in-6 Fiber Configuration for Intracellular Single-Cell pH Measurement.
abstract: Single-cell research is essential for understanding cell heterogeneity, cell differentiation, and carcinogenesis, among other important cellular processes. New techniques for intracellular pH monitoring are urgently needed to gain new insights into single-cell responses to external stimuli. In this study, fiber-optic reflection-based pH micro (μ)-probes (tip diameter: 500-3000 nm) were designed and fabricated using a novel hexagonal 1-in-6 fiber configuration. An organic-modified silicate (OrMoSils) sol-gel doped with a pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), were coated onto the probe sensing tip for pH detection. These probes enabled neutral pH monitoring and quasi-real-time data acquisition (response time: 20 ± 5 s). The fluorescence signals of the newly developed probes were found to correlate linearly with pH (R(2) = 0.9869 when coupling laser power was at 8.2 mW) within a biologically relevant pH range (6.18-7.80). The pH resolution was 0.038 pH unit. The miniaturized probes were validated in single human lung cancer A549 cells to demonstrate applicability in single-cell experiments. In summary, novel pH μ-probes with excellent resolution and response times within a biologically relevant pH range were developed, and they can be used for measuring pH changes in single cells.
authors.affiliation: †Department of Chemistry and Center for Single Nanoparticle, Single Cell, and Single Molecular Monitoring, Missouri University of Science and Technology, Rolla, Missouri 65409, United States.
authors.forename: Qingbo
authors.initials: Q
authors.lastname: Yang
authors.affiliation: ‡Department of Electrical and Computer Engineering, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Hanzheng
authors.initials: H
authors.lastname: Wang
authors.affiliation: †Department of Chemistry and Center for Single Nanoparticle, Single Cell, and Single Molecular Monitoring, Missouri University of Science and Technology, Rolla, Missouri 65409, United States.
authors.forename: Sisi
authors.initials: S
authors.lastname: Chen
authors.affiliation: ‡Department of Electrical and Computer Engineering, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Xinwei
authors.initials: X
authors.lastname: Lan
authors.affiliation: ‡Department of Electrical and Computer Engineering, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Hai
authors.initials: H
authors.lastname: Xiao
authors.affiliation: †Department of Chemistry and Center for Single Nanoparticle, Single Cell, and Single Molecular Monitoring, Missouri University of Science and Technology, Rolla, Missouri 65409, United States.
authors.forename: Honglan
authors.initials: H
authors.lastname: Shi
authors.affiliation: †Department of Chemistry and Center for Single Nanoparticle, Single Cell, and Single Molecular Monitoring, Missouri University of Science and Technology, Rolla, Missouri 65409, United States.
authors.forename: Yinfa
authors.initials: Y
authors.lastname: Ma
mesh_terms: D004566:Electrodes; D005336:Fiber Optic Technology; D005452:Fluoresceins / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017646:Organosilicon Compounds / Q000737:chemistry*; D059010:Single-Cell Analysis / Q000295:instrumentation* / Q000379:methods*
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; D017646:Organosilicon Compounds; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein