Bromocresol Green-Based Optimized Colorimetric Sensors for Albumin and Atropine

Introduction

Bromocresol green (3,3',5,5'-tetrabromo-m-cresolsulfonphthalein;Figure 1) is a triphenylmethane dye belonging to the sulfonephthalein class of indicators. Bromocresol Green structure belongs to sulfonephthalein triphenylmethane framework with four bromine atoms substituted on two m-cresol rings. It is widely utilized in various scientific applications, including as a pH indicator in microbiological growth media and titrations, and for the colorimetric determination of serum albumin. The synthesis of bromocresol green is primarily achieved through the electrophilic bromination of m-cresol purple (m-cresolsulfonphthalein). However, commercial preparations of bromocresol green often contain impurities that can affect the accuracy of sensitive analytical measurements. Therefore, robust purification methods are essential to obtain high-purity bromocresol green for demanding applications.[1] Bromocresol green is a bio-based dye with a yellow-green to blue-green color. Bromocresol green turns yellow (λmax=435 nm, protonated form) when placed in acidic solution (e.g. pH=4.15), and turns blue in basic solution (λmax=615 nm, deprotonated form). Bromocresol green is widely used as a pH indicator in the field of biochemical analysis. In addition, Bromocresol green is also used to detect the concentration of molecules such as creatinine, and to judge the viability of cells.[2-3]

Bromocresol Green Colorimetric Sensor for Albumin Optimized via Chemometrics

The detection of human serum albumin (HSA) in urine is crucial for the early diagnosis of nephrotic syndromes and diabetic nephropathy. Franceschi et al. developed a Colour Catcher® (CC)-based colorimetric sensor (2 × 2.5 cm) able to detect albumin in synthetic samples by exploiting the well know reaction between the protein and Bromocresol Green (BCG) [36], anciently defined as “protein error”. Such reaction results in a visible colour change from yellow to blue at proper pH values. Design of Experiment (DoE) technique was applied to optimize impactful experimental conditions in sensors preparation and sample analysis; subsequently, colorimetric and spectrophotometric detection were tested by submitting to multivariate analysis the respective outputs (RGB coordinates or UV–Vis spectra). Qualitative recognition of albumin was achieved by applying probabilistic classification tools (Linear (LDA) and Quadratic (QDA) Discriminant Analysis) to score values computed by the means of Principal Components Analysis (PCA). Finally, a preliminary assessment of LOD for both detection techniques was conducted by predicting samples at lower BSA concentrations and identifying the lowest concentration level correctly predicted. The optimized sensor proved a detection limit as low as 0.5 μM for albumin, making it a promising candidate for rapid, low-cost, and user-friendly point-of-care (PoC) applications.[4]

Bromocresol Green-Based Dual Colorimetric-Electrochemical Sensing for Atropine

Atropine is a tropane alkaloid derived from plants in the Solanaceae family, such as Atropa belladonna (deadly nightshade) and Datura stramonium (jimson weed). Atropine is frequently used in medical settings, as an antidote for organophosphate poisoning, to treat bradycardia and gastro-intestinal spasms, and in ophthalmology to dilate the pupils (mydriasis). In therapeutic amounts, atropine is safe and effective, but in excessive doses, it can cause serious symptoms such as hallucinations, agitation, tachycardia, hyperthermia, urinary retention, dry skin, and, in extreme cases, coma and death. Due to these toxic properties at high doses, atropine has been reported in assassination attempts. Melo et al. propose a novel dual-mode analytical platform that combines screen-printed graphite electrodes with square-wave voltammetry and a colorimetric reaction using bromocresol green. This dual platform provides three distinct analytical responses: a colour change via the colorimetric reaction and electrochemical responses before and after the colorimetric reaction, allowing robust atropine identification. For the first time, the electrochemical behaviour of atropine in the presence of bromocresol green has been investigated, with mechanistic insights elucidated through NMR analysis. Although atropine alone undergoes an irreversible oxidation process,the colorimetric reaction facilitates a redox process involving bromocresol green, allowing indirect atropine detection. The real-world applicability of this dual-sensing platform is demonstrated by detecting atropine in drink and biological samples for potential spiking and poisoning diagnosis. Importantly, the platform is shown to function within solutions containing quinine, proving its suitability to analysing strong and bitter tonic water drink with low atropine concentrations, overcoming this known analytical problem. The developed method exhibited a wide linear range (0.001-0.4 mg/mL), a low limit of detection (0.255μg/mL), and excellent stability with relative standard deviation lower than 7 %. Interference studies confirm the method’s selectivity,and atropine recoveries from drink and biological samples were close to 100 %. The proposed platform is a simple, rapid, and selective screening tool, and shows significant potential for forensic applications in atropine detection. [5]

References

[1] BenchChem. A technical guide to the synthesis and purification of bromocresol green. BenchChem; 2025.

[2] Delanghe S, et al. Binding of bromocresol green and bromocresol purple to albumin in hemodialysis patients. Clin Chem Lab Med. 2018 Feb 23;56(3):436-440.

[3] Jurmanović S, et al. Organically modified silicate thin films doped with colourimetric pH indicators methyl red and bromocresol green as pH responsive sol–gel hybrid materials[J]. Thin Solid Films, 2010, 518(8): 2234-2240.

[4] Franceschi G E , Magnaghi L R , Guembe-Garcia M ,et al.Enhancing albumin detection with Chemometrics: A multivariate approach to Bromocresol Green-based Colorimetric sensor development[J].Chemometrics and Intelligent Laboratory Systems, 2025, 262.DOI:10.1016/j.chemolab.2025.105400.

[5] Melo LMA, Bernalte E, Crapnell RD, Verly R, Whittingham MJ, Munoz RAA, dos Santos WTP, Banks CE. A dual colorimetric-electrochemical platform based on bromocresol green for the selective detection of atropine. Sens Actuators B Chem. 2025;441:137962. doi:10.1016/j.snb.2025.137962