Sandeep Mariserla,
Graduate student in Materials Science and Technology

My research focus is on developing biosensors using inverse opal hydrogel structures. Biosensor experiments^(1,2) involve immobilizing one reactant on a surface and monitoring its interaction with a second component in solution. In general, biosensors consist of two components: a highly specific recognition element and a transducer that converts the molecular recognition event into a quantifiable signal. Our strategy is to employ various biologically sensitive components, i.e. enzymes, proteins, synthetic molecules, antibodies etc., into mesostructured three-dimensional (3D) structures known as colloidal crystals.
Colloidal crystals with 3D translational order can be formed from suspension by self-assembly methods such as patterned sedimentation, controlled evaporation, sonication and other methods. These colloidal crystals have been utilized to template the growth of mesostructured semiconductors, metals, and polymers. Because the colloidal template has a characteristic spacing of the order of hundreds of nanometers, the resulting structure interacts strongly with visible and infrared light, leading to optical diffraction that follows Bragg’s law ⁽³⁾.
Periodic hydrogel structures (Fig.1) are especially interesting because hydrogels may be functionalized to respond to a variety of physical and chemical stimuli by changing their dimensions. When tailored correctly, such response in a 3D structure can lead to large shifts in the Bragg diffraction wavelength, thus creating functional materials with tunable optical properties. By incorporating the specific recognition element into a inverse opal hydrogel, an optically tunable biosensor can be realized.

Figure 1. SEM images of mesostructured hydrogel structures made from a colloidal crystal template.

References:
1. W. Qian, Z. -Z. Gu, A. Fujishima & O. Sato, Langmuir, 18, 4526-4529 (2002).
2. T. Miyata, N. Asami & T. Uragam, Nature, 399, 766-769 (1999).
3. Y. -J. Lee & P. V. Braun, Adv. Mater., 15, 563-566 (2003).