Near-Infrared Fluorescence Detection of Acetylcholine in Aqueous Solution Using a Complex of Rhodamine 800 and p-Sulfonato-calix[8]arene

Abstract

The complexing properties of p-sulfonatocalix[n]arenes (n = 4: S[4], n = 6: S[6], and n = 8: S[8]) for rhodamine 800 (Rh800) and indocyanine green (ICG) were examined to develop a near-infrared (NIR) fluorescence detection method for acetylcholine (ACh). We found that Rh800 (as a cation) forms an inclusion complex with S[n], while ICG (as a twitter ion) have no binding ability for S[n]. The binding ability of Rh800 to S[n] decreased in the order of S[8] > S[6] >> S[4]. By the formation of the complex between Rh800 and S[8], fluorescence intensity of the Rh800 was significantly decreased. From the fluorescence titration of Rh800 by S[8], stoichiometry of the Rh800-S[8] complex was determined to be 1:1 with a dissociation constant of 2.2 μM in PBS. The addition of ACh to the aqueous solution of the Rh800-S[8] complex caused a fluorescence increase of Rh800, resulting from a competitive replacement of Rh800 by ACh in the complex. From the fluorescence change by the competitive fluorophore replacement, stoichiometry of the Rh800-ACh complex was found to be 1:1 with a dissociation constant of 1.7 mM. The effects of other neurotransmitters on the fluorescence spectra of the Rh800-S[8] complex were examined for dopamine, GABA, glycine, and l-asparatic acid. Among the neurotransmitters examined, fluorescence response of the Rh800-S[8] complex was highly specific to ACh. Rh800-S[8] complexes can be used as a NIR fluorescent probe for the detection of ACh (5 × 10−4−10−3 M) in PBS buffer (pH = 7.2).

Derquantel and abamectin: Effects and interactions on isolated tissues of Ascaris suum

“…When the two inhibitors are applied together the action at the two different putative sites of action on the nAChR combine and the effects are greater than additive at high (> 10 μM) concentrations of acetylcholine. At vertebrate neuro-muscular junctions, the released acetylcholine concentration can reach as high as 5 mM [40]. Hence, the inhibition of acetylcholine response at the somatic muscle of the worm produced by the combination may be higher than we have observed here.…”

“…We selected 1 μM derquantel for testing based on reports of intestinal (extra-worm) concentration of 13 μM at 12 hours [38] and the likely decrease in concentration of the drug within the worm [40]. We have seen that the effects of derquantel have a rapid onset and the drug behaves in a competitive manner with acetylcholine, suggesting a site of action on the extracellular surface of the nAChR.…”

A step toward simplified detection of serum albumin on SDS-PAGE using an environment-sensitive flavone sensor

“…39 In this case, the fluorescence enhancement of compounds 1–6 in the presence of 1.0 mg/ml of BSA was 7 ~ 1100 fold (Table S2, ESI†). Therefore, the detection limits of compounds 1–6 were 2.6, 0.14, 0.59, 0.09, 14, and 3.4 μg/ml, respectively.…”

Advanced materials for optical sensing and biosensing of neurotransmitters

“…In addition, Jin [94] used the complexing ability of calixarenes with rhodamine 800 (Rh800) and indocyanine green (ICG) for photometric detection of ACh in aqueous solution with an LOD of 5 × 10 -4 M. Production of complex between Rh800 and calixarenes (S [8]) caused a decrease in the fluorescence intensity of the Rh800. Upon adding ACh to the Rh800-S [8] complex, the fluorescence intensity of Rh800 in the NIR region increased linearly, with the fluorescence intensity of the Rh800-S [8] complex being highly sensitive to ACh over DA, GABA, glysine, and L-aspartate.…”