Colorimetric chemosensor based on a carminic acid and Pb2+ complex for selective detection of cysteine over homocysteine and glutathione in aqueous solution

Colorimetric Detection of ATP by a Chlorophosphonazo III -based Mg2+ Complex in Aqueous Solution via Indicator Displacement Approach

A simple and effective colorimetric detection of adenosine 5-triphosphate (ATP) in 100% aqueous media was developed based on an indicator displacement approach (IDA). A commercially available dye, Chlorophosphonazo III (CPA), was utilized as the indicator and the ATP detection was achieved using the complex of CPA with Mg²⁺ in a 2:1 stoichiometric ratio (CPA₂-Mg²⁺) through the regeneration of CPA by the binding of ATP to Mg²⁺. Upon addition of a series of anions to the CPA₂-Mg²⁺ complex, only the appearance of the solution of the complex with ATP exhibited a color change from blue to purple which can be detected by the naked eye. Moreover, the ATP recognition was not hampered by the presence of other anions. Hence, CPA₂-Mg²⁺ is efficient in ATP highly selective and sensitive colorimetric detection in 100% aqueous media.

Colorimetric detection of homocysteine by a pyridylazo dye-based Cu2+ complex via indicator displacement mechanism

A BrPAPS based Cu²⁺ complex has been developed as a colorimetric probe for the selective recognition of homocysteine (Hcy) over cysteine (Cys) and glutathione (GSH) in an aqueous solution via the indicator displacement assay. BrPAPS formed a complex with Cu²⁺ in a 1:1 ratio (BrPAPS-Cu²⁺) accompanied by the color change from yellow to red. Detecting Hcy is based on high affinity of Hcy for Cu²⁺. The addition of Hcy to BrPAPS-Cu²⁺ caused the complex formation of Hcy with Cu²⁺ in a 2:1 stoichiometry, resulting a hypsochromic shift with change back of color from red to yellow by the release of BrPAPS from BrPAPS-Cu²⁺. The absorption response is linear with the Hcy concentration in the range of 0-20 μM with a detection limit of 1.46 μM. Moreover, the detection of Hcy was not significantly affected by other amino acids from the competition experiments. Thus, BrPAPS-Cu²⁺ can be used as a simple probe for Hcy in aqueous solution.

A Simple Distance Paper-Based Analytical Device for the Screening of Lead in Food Matrices

A simple and rapid distance paper-based analytical device (dPAD) for the detection of lead (Pb) in foods is proposed herein. The assay principle is based on competitive binding between carminic acid (CA) and polyethyleneimine (PEI) to Pb in a food sample. The paper channels were pre-immobilized with PEI, before reacting with a mixture of the sample and CA. Pb can strongly bind to the CA; hence, the length of the red color deposition on the flow channel decreased as a lower amount of free CA bound to PEI. The dPAD exhibited good linear correlation, with ranges of 5-100 µg·mL-1 (R2 = 0.974) of Pb. Although, the limit of detection (LOD) of this platform was rather high, at 12.3 µg·mL-1, a series of standard additions (8.0, 9.0, and 10.0 µg·mL-1) can be used to interpret the cutoff of Pb concentrations at higher or lower than 2 µg·mL-1. The presence of common metal ions such as calcium, magnesium, nickel, and zinc did not interfere with the color distance readout. The validity of the developed dPAD was demonstrated by its applicability to screen the contamination of Pb in century egg samples. The results obtained from the dPAD are in accordance with the concentration measured by atomic absorption spectroscopy (AAS) (n = 9). In conclusion, this proposed dPAD, combined with the standard addition method, could be applied for screening Pb contamination in food matrices. This platform is, therefore, potentially applicable for field measurements of Pb in developing countries, because it is cheap and rapid, and it requires no significant laborious instruments.