Design and Investigation of a Series of Rhodamine-Based Fluorescent Probes for Optical Measurements of pH

Abstract

A series of structurally similar fluorescent probes (1-4), synthesized from rhodamine B, were designed to optically measure pH. Each probe had a unique "off-on" response as the solution went from basic to acidic. Probes 1-3 exhibited a spiro-cyclic quenching of the pyronin B fluorophore, whereas probe 4 is quenched by PET from the amine moiety.A chemical sensor capable of measuring pH by optical methods has important implications in analytical and biological chemistry. Fluorescence based probes have demonstrated a superior ability in the detection of various analytes with high sensitivity and low detection limits. In cellular biology, the pH of specific and localized areas of the cell can be an important indication of cellular events.1 Such information could potentially be useful in the diagnosis of specific diseases. For example, colorectal cancer,2 breast cancer2b , 3, cystic fibrosis,4 and neurodegenerative disorders5 have all been linked to abnormal pH regulation, resulting in localized pH values of 4.5-6.0 that are referred to as the acidic window. Currently, a large number of fluorescence based pH sensors have been reported in the literature and are commercially available.6 However, many of these probes lack sensitivity or are simply non-responsive in the so-called "acidic window". Therefore, it would be of great benefit to aid in the diagnosis of these diseases by developing new and more sensitive probes for the measurement of pH.Many fluorescent probes operate in an "off-on" fashion, where in the "off" state the fluorescence is quenched, while the "on" state the fluorophore is fully fluorescent with a high quantum yield. Among the many fluorophores that potentially could be used as pH sensors, pyronin B has particular advantages in biological imaging because of its high quantum yield (Φ= 0.35), longer excitation and emission wavelength (550-600 nm), spectral insensitivity to solvent polarity, pH, and a high tolerance to photobleaching.7 With these criteria in mind, we set out to design a mode of regulating the fluorescence of this fluorophore by synthesizing various benzylamine derivatives at the 9-position, which have Correspondence to: Daniel J. Dyer, ddyer@chem.siu.edu. Supporting Information Available: Detailed synthetic procedures and spectra. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access Author ManuscriptOrg Lett. Author manuscript; available in PMC 2011 July 16. Starting with commercially available rhodamine B, we synthesized various benzylamine structures; (see supporting information for synthesis details), where the amine moiety is primary, secondary, and tertiary ( Figure 1). The rhodamine-based literature is rife with fluorescent probes that are regulated by a spirocyclic structure. These spirocyclic compounds lack absorbance and fluorescence, in visible spectrum, when engaged in the spirocyclic form but will open upon binding to specific analytes to restore the fluorophore and fluorescence intensity of that compound. Typically, th...

Pyrene or rhodamine derivative–modified surfaces of electrospun nanofibrous chemosensors for colorimetric and fluorescent determination of Cu 2+ , Hg 2+ , and pH

“…Cu 2+ is the third most abundant essential transition metal ion in the human body, and it plays a major role in various biological processes [11,12]. Fluorescent chemosensors based on rhodamine B derivatives (RhBs) and pyrenederivatives (Pys) are both satisfactory probes for sensing various HTM cations including Hg 2+ , Cu 2+ , and pH because of their unique properties such as a high fluorescence quantum yield, a high absorption coefficient, and high sensitivity [13][14][15][16][17][18][19][20]. However, most of the mentioned studies have focused on the solution, thin film, and bulk solid states [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Optical Tracking of Phagocytosis with an Activatable Profluorophore Metabolically Incorporated into Bacterial Peptidoglycan

“…We previously reported the use of rhodamine-lactams for imaging of lysosomal acidity and lysosomal pH based tumor imaging. [13][14][15][16][17][18][19][20][21][22] Herein rhodamine-lactams were conjugated with bacterium-homing entities to envelope rhodamine-lactams within bacteria for reporting phagolysosomal acidity during bacterial phagocytosis.…”

The study of a curcumin-resembling molecular probe for the pH-responsive fluorometric assay and application in cell imaging

“…Compared with the other pH i measurement methods such as microelectrodes, NMR, and absorbance spectroscopy, the fluorescence measurement of the pH i value by the pH-dependence fluorescent probe has the advantages of the high sensitivity, high spatial resolution, synchronicity, nondestructive inspection, simple operation and low cost [7]. Best et al designed and investigated series of rhodamine-based fluorescent probes for optical measurements of pH, in which probes exhibited a spirocyclic quenching of the fluorophore [8]. Yuan et al developed rhodamine amide derivatives that systematically tuned the pK a values and employed them to detect acidic pH variations in living Hela cells with a turn-on signal [9].…”