Various carboxyl anions play important roles in biological systems, biomedical science, and the food industry. For example, Glutamate can excite cells to death, called excitotoxicity. Food should be monitored because it is used as a flavor and taste enhancer. Tartaric acid is often used as an acidulant in beverages and food. However, it is a muscle toxin, and excessive consumption may cause paralysis and death. Citrate is another carboxyl anion whose presence in urine is considered to inhibit the crystallization of calcium salt. Its high concentration in urine indicates the growth of kidney stones and urological diseases such as nephrolithiasis and hypocitraturia. The presence of oxalate in the human diet is important because it influences the bioavailability of dietary calcium and magnesium. Since there is no enzyme in the human body to degrade oxalate, an increased amount of dietary oxalate significantly decreases calcium and magnesium absorption by forming insoluble oxalate salts, which finally accumulate in the renal tissue. It may result in several pathological conditions, including renal failure, pancreatic insufficiency, and the development of kidney stones. Therefore, the quantitative information of oxalate is widely used in identifying several diseases, including hyperoxaluria, vulvodynia, and kidney stones. Many methods have been developed for quantitative analysis of carboxyl anions, which may not be suitable for general purposes. However, colorimetric and fluorescence sensing through indicator displacement assay (IDA) of a specific anion becomes an attractive research area because of its low cost, simplicity, and visual detection of anions without expensive instruments. The IDA is based on the competitive binding of an indicator and an analyte to a receptor. In this protocol, when the indicator binds with the metal-ligand complex receptor, its color and fluorescence are found to be changed. When a competitive anion could replace the dye from the receptor-dye inclusion, the color and fluorescence of the dye are restored. In this research to detect carboxylate anions, the thiophene-based polyamine macrocycle was synthesized by Schiff's base reaction between 2,2'-diamino-N-methyldiethylamine and 2,5-thiophenedicarboxaldehyde in high dilution condition followed by sodium borohydride reduction. Then, this macrocycle was converted to dinuclear Ni(II) complex (M) and studied for recognition of carboxylate anions by indicator displacement assay (IDA) using several commercially available dyes Eosin Y, Pyrogallol Red, and Pyrocetochol Violet. The chemosensor showed selectivity for citrate and oxalate over common anions (fluoride, chloride, bromide, iodide, nitrate, perchlorate, sulfate, and phosphates) at physiological pH by restoring the original color of dyes. The fluorescence quenching titration of Eosin Y with M showed a binding constant log K = 4.85, and the fluorescence enhancement titration showed a binding constant of log K= 4.49 for citrate and log K= 4.45 for oxalate. In this poster presentation, the work will be explained in detail.