Poly(acrylic acid) Hydrogel Microspheres for a Metal-Ion Sensor.

Area of Science:

• Materials Science
• Analytical Chemistry
• Biomedical Engineering

Background:

• Accurate detection of divalent metal ions like calcium (Ca²⁺) and magnesium (Mg²⁺) is crucial for diagnosing various physiological conditions.
• Existing methods for measuring Ca²⁺ and Mg²⁺ in biofluids often face challenges with interference and complex sample preparation.

Purpose of the Study:

• To develop a novel microfluidic sensor for the simultaneous detection of Ca²⁺ and Mg²⁺ in human saliva and serum.
• To utilize cross-linked poly(acrylic acid) (PAA) X-droplets as responsive elements for ion sensing.
• To establish a method that overcomes the interference issues commonly encountered in biofluid analysis.

Main Methods:

• Monodispersed cross-linked poly(acrylic acid) (PAA) X-droplets were fabricated using microfluidics and in situ UV curing.
• PAA X-droplets treated with KOH (PAA_KOH X-droplets) were employed as sensors, with their size changes monitored in a poly(dimethylsiloxane) (PDMS) channel.
• The sensor's response was characterized by measuring the saturated diameter ratio (R_sat-dia) and the inverse time to reach half saturated diameter reduction (T_1/2^-1) as a function of divalent metal ion concentration.

Main Results:

• PAA_KOH X-droplets exhibited a concentration-dependent shrinkage upon exposure to Ca²⁺ and Mg²⁺ ions.
• The speed of droplet size reduction (T_1/2^-1) linearly correlated with the concentration of individual Ca²⁺ and Mg²⁺ ions.
• The saturated diameter ratio (R_sat-dia) and T_1/2^-1 allowed for the successful and accurate quantification of both Ca²⁺ and Mg²⁺ in mixed solutions and biological samples like saliva and serum.

Conclusions:

• The developed PAA X-droplet sensor provides a simple, cost-effective, and highly accurate method for simultaneous Ca²⁺ and Mg²⁺ detection.
• This sensing approach effectively resolves the interference challenges in measuring Ca²⁺ in the presence of Mg²⁺ within biofluids.
• The microfluidic sensor demonstrates significant potential for point-of-care diagnostics and routine clinical analysis of essential metal ions.