Bits and Pieces_02/01/10

Came across three papers that I thought are relevant to Biosensors and may be worth talking about a bit.

Bromomaleimides for Protein Conjugation
in recent JACS issue takes the maleimide chemistry to next level. Maleimide group reacts with thiols and is commonly used for protein immobilization and labeling. The new report uses bromo/dibromo maleimides and offer three advantages over conventional reaction

  1. Reaction is reversible in presence of large excess of thiols/phosphines
  2. Dibromo maleimides can be inserted into a disulfide bond to form maleimide bridge OR a second thiol group can be attached for added functionality
  3. Functional group can also be inserted, like in traditional maleimides, to the nitrogen

 

Credit: J. Am. Chem. Soc., DOI: 10.1021/ja908610s

Authors summarized their results best- “We envisage numerous potential applications for bromomaleimides incorporating functional groups, including biotin or solid supports for protein purification and immobilization; fluorophores, radiolabels, and quantum dots for imaging; polymers, e.g., PEG, for protein stability and others.”

Phosphorescent Mn-doped ZnS quantum dots (QDs) for Glucose Sensing. This I thought is pretty slick! Stick glucose oxidase enzyme (GOD) on phosphorescent QDs –no big deal! When glucose is present, GOD changes it into gluconic acid and hydrogen peroxidase. Peroxidase quenches QD’s phosphorescence proportional to the amount of glucose and can be measured at an excitation wavelength of 290 nm and an emission wavelength of 595 nm. Biosensor can detect glucose directly in serum sample but there is catch that author’s themselves point out – “The developed sensor displays relative high sensitivity and good selectivity, but it is difficult to be re-engineered, and the interaction of H2O2 with QDs requires a relatively long time (15 min).”

Thermally Addressed Immunosorbent Assay. The assay is identical to your conventional sandwich immunoassay except the detection tags on secondary antibodies, instead of being enzyme or fluorescent dye, are phase change nanoparticles. The solid to liquid phase change absorbs heat energy and have sharp melting curves. The peak of melting curve is proportional to amount of nanoparticles which is proportional to the 2nd antibody. According to authors- “The signal transduction is based on a known but unexplored phenomenon: the temperature of a single component solid does not rise over its melting point until the entire solid is molten, thus the melting peak of the solid is sharp after a linear temperature rise process.” Multiplexing is possible because various nanoparticles with different melting curves can be used. In the present paper indium, lead-tin, and tin nanoparticles with melting temperatures of 156, 183, and 230 °C respectively were used.

Can this method compete with other multiplexing technologies? Probably not! But concept is neat especially if it can be combined with work from Michael Roukes lab in Caltech.

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