Beetroot-Pigment-Derived Colorimetric Sensor for Detection of Calcium Dipicolinate in Bacterial Spores

Abstract

In this proof-of-concept study, we describe the use of the main red beet pigment betanin for the quantification of calcium dipicolinate in bacterial spores, including Bacillus anthracis. In the presence of europium(III) ions, betanin is converted to a water-soluble, non-luminescent orange 1∶1 complex with a stability constant of 1.4×105 L mol–1. The addition of calcium dipicolinate, largely found in bacterial spores, changes the color of the aqueous solution of [Eu(Bn)+] from orange to magenta. The limit of detection (LOD) of calcium dipicolinate is around 2.0×10–6 mol L–1 and the LOD determined for both spores, B. cereus and B. anthracis, is (1.1±0.3)×106 spores mL–1. This simple, green, fast and low cost colorimetric assay was selective for calcium dipicolinate when compared to several analogous compounds. The importance of this work relies on the potential use of betalains, raw natural pigments, as colorimetric sensors for biological applications.

Fluorescent bioinspired protein labeling with betalamic acid. Derivatization and characterization of novel protein-betaxanthins

“…This has opened up new possibilities for the study of signalling between flowers and pollinators [13,21]. Other potential applications of betalains are their use in microscopy as a new probe for live cell imaging [13,22] and as a sensor for colorimetric assays [23]. carried out according to a previous methodology with some modifications [24].…”

Betalains: from the Colors of Beetroots to the Fluorescence of Flowers

“…77 A protonação das porções carboxílicas da betanina (pK a = 3,5) ou a adição de quelantes adequados (e.g., EDTA ou EGTA) deslocam o equilíbrio no sentido da betanina livre, indicando a formação de complexos. Complexos 1:1 de betanina e íons Eu(III) (log K para Bn:Eu(III): 5,2) 78 foram caracterizados e usados na quantificação de esporos de Bacillus anthracis, o agente causador do carbúnculo. A concorrência entre a porção 1,2,3,4-tetrahidro-2,6-dipicolina presente nas betalaínas (Figura 5) e o sal de cálcio do ácido dipicolínico (CaDPA) presente no microrganismo por íons Eu 3+ pode ser monitorada pela mudança de cor da solução de [Eu(Bn)] + de amarelo para vermelho quando submetida à presença de CaDPA.…”

“…A concorrência entre a porção 1,2,3,4-tetrahidro-2,6-dipicolina presente nas betalaínas (Figura 5) e o sal de cálcio do ácido dipicolínico (CaDPA) presente no microrganismo por íons Eu 3+ pode ser monitorada pela mudança de cor da solução de [Eu(Bn)] + de amarelo para vermelho quando submetida à presença de CaDPA. 78 Betalaínas também foram utilizadas como ponto de partida para o desenvolvimento de uma sonda fluorescente que é capaz de marcar eritrócitos infectados com Plasmodium falciparum, o agente causador da malária em humanos. 20 A Figura 6 mostra que a indicaxantina não marca os eritrócitos, estejam eles infectados ou não com P. falciparum.…”

Revisiting the Mechanism of Hydrolysis of Betanin

“…Due to its photoredox properties and binding strength of its carboxylic acid groups with metal oxides, for example, TiO 2 and ZnO, betanin has been used for the development of dye-sensitized solar cells and photocatalytic hydrogen production (10)(11)(12)(13)(14)(15)(16)(17). The ability of betanin as a metal ion ligand has been further explored in the development of colorimetric sensors for calcium dipicolinate in bacterial spores (18). Additionally, betanin has been used as a starting material for the synthesis of two-photon absorbing fluorescent probes (19,20) and fabrication of nanoparticles (21,22).…”