Ion-selective optodes based on near infrared fluorescent chromoionophores for pH and metal ion measurements

Highly stable near infrared fluorescent (NIRF) boron-dipyrromethene (BODIPY) derivatives have been utilized as chromoionophores in ion-selective optodes for the first time. The pKa values of the chromoionophores are tuned by using different substituted aniline groups. The derivative with dimethyl aniline group has pKa value of 2.5 in plasticized poly (vinyl chloride) membrane, while the more basic piperidine group gives larger pKa value of 5.4. Ion optodes prepared with NIRF chromoionophores and cation exchanger are pH sensitive and exhibited fully reversible response. With additional ionophore such optodes can measure the concentration of metal ion based on ion exchange mechanism and exhibited comparable dynamic range and selectivity to the optodes containing traditional ETH types of chromoionophores. Fluorescence measurements in near infrared region between 700 and 900 nm minimize the influence of autofluoresence and background absorption, resulting in more sensitive and precise detection. The proposed optodes had been applied for pH measurement in blood samples.