Paper-based microfluidics for experimental design: screening masking agents for simultaneous determination of Mn(II) and Co(II)

This work describes an efficient, generalizable approach towards the identification (and mitigation) of interferences for colorimetric detection using microfluidic paper-based analytical devices. Colorimetric detection is commonly used in conjunction with microfluidic paper-based analytical devices; however, many colorimetric reagents lack selectivity. The selectivity problem is particularly true for metal detection where colorimetric ligands can complex with multiple metals. Many solution-based studies have investigated methods to mask interfering metals, but solution-based procedures do not always apply to paper sensors where the reagents are dried and the cellulosic functional groups may also interact with metals. Here, a simple eight-armed microfluidic paper-based analytical device has been designed to rapidly screen masking agents for the detection of transition metals using the non-specific colorimetric ligand 4-(2-pyridylazo)resorcinol as a model system to optimize conditions. The combination of dimercaptosuccinic acid and triethylenetetramine in pH 10 borate buffer was identified for selective determination of Mn(II) with greater than 87% masking of interfering metals. A combination of ethylenediaminetetracetic acid and triethylenetetramine in pH 10 phosphate buffer was identified for selective determination of Co(II) with greater than 96% masking for most of the interfering metals although Fe(II), Fe(III), and Ni(II) still interfere. While used for this specific system, the approach described here is generalizable for ligand and interference screening with potential applications to a number of different assays performed on mu PADs.