One-step, room temperature, colorimetric detection of mercury (Hg2+) using DNA/nanoparticle conjugates.

Because of the increasing threat of mercury exposure in the environment from global mercury emissions as well as various forms of contamination,1 there has been a growing interest in the development of highly sensitive and selective systems for mercuric ions (Hg2+) over the past few years. Various sensor systems for detection of Hg2+, based upon organic chromophores or fluorophores,2 conjugated polymers,3 oligonucleotides,4 DNAzymes,5 proteins,6 thin films,7 and nanoparticles (NPs),8 have been reported. Most of these systems, however, have either limitations with respect to sensitivity, selectivity, and simplicity or the need of electronic read-out circuits for substantial sensitivity. Mirkin et al. recently reported colorimetric detection of Hg2+ in aqueous media using DNA-functionalized gold NPs.8 This visual inspection method is highly selective and sensitive and also simpler than conventional methods except for the requirement of an electronic heating element coupled to the sensor system for careful monitoring of thermal denaturation temperature during the detection process.8 The need of an electronic heating and read-out unit for Hg2+ detection at elevated temperatures clearly makes this system relatively costly and impractical for fast on-the-spot sample assays. Therefore, it should be highly desirable to develop a detection system that is not only sensitive and reliable but also simple, practical, and economical in its operation. To achieve this goal, we have taken a fundamentally different design, making use of DNA/NP conjugates and thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry9 to develop a sensor system that operates within an adjustable operating temperature range and rapidly detects mercury in a single step. The basic design of our sensor system for Hg2+ is composed of three elements as shown in Scheme 1. We first prepared two types