The Research And Application Of Gold Nanomaterials In Biosensing

In recent years, nanotechnology has become one of the most exc iting forefront fields in analytical chemistry. A wide variety of nanomaterials, such as nanoparticles, nanowires, nanotubes, nanorods, nanocomposites and semiconductor quantum dots(QDs), have found broad applications in many kinds of analytical methods. Owing to their small size(normally in the range of 1-100 nm), large surface-to-volume ratio, nanomaterials exhibit unique electronic, optical and chemical properties which are different from those of bulk materials, such as surface effect, small size effect, quantum size effect, macro quantum tunnel effect and so on, and they can be widely used to fabricate a variety of novel and improved chemosensors and biosensors. Among these nanomaterials, gold nanomaterials possess excellent properties such as facile synthesis, high stability, easy surface modification and tunable wavelengths in surface plasmon resonance. Due to these properties, they have received considerable attention in the past twenty years and been widely applied in the development of bioanalytical sensing techniques. Importantly, the introduction of gold nanomaterials not only enhanced the selectivity, sensitivity and reproducibility of sensing techniques, but also produced a lot of new principles and methods. Based on these features, we have developed a series of novel biosensing systems using gold nanomaterials for analysis of blood glucose, small mocular, and activity of enzyme which are associated with human health. The main points are summarized as follows:(1) We described a novel strategy for rapidly mediating the size of gold nanorods based on the oxidative etching ability of hydroxyl radical( ·OH). It has been reported that H2O2 at high concentration can oxidize the GNRs directly, and ·OH has much stronger oxidizing ability than H2O2. Therefore, the introduction of ·OH to the reaction of oxidative etching of GNRs could significantly shorten the etching time. Experimental investigation showed that GNRs directly oxidized by 10 m M and 1 m M H2O2 required 12 h and longer time, respectively. In contrast, ·OH generated by Fenton reaction oxidized gold nanorod in the range of minutes to a few hours, which significantly lowered the time and cost of fabrication. By utilizing this method, different sizes of GNRs have been obtained through the oxidative etching of large GNRs with narrow size distributions, avoiding the high batch-to-batch variability of size of GNRs. Furthermore, this strategy possesses advantages such as mild reaction conditions and no requirement for thermal heating(2) We developed a novel plasmonic blood glucose biosensor based on glucose oxidase(GOx)-mediated oxidative etching of gold nanorods. Taking advantage of GOx, the enzymatic etching of GNRs was realized by coupled reaction of glucose oxidation to H2O2 and ·OH generation by Fenton reaction, causing a blue shift of the longitudinal surface plasmon resonance peak and color changes of the GNRs, and achieved the goal to visual detection of glucose. This assay possesses a linear range from 0.1 to 1 m M and a detection limit of 0.1 m M. By increasing the concentration of Fe2+-EDTA, the detection time could shorten to only 15 min, the detection linear range was changed from 1 to 8 m M, the detection limit was changed to 1 m M. Under this condition, the normal level of glucose in blood was just in this linear range, it has improved the mothod for quick and convenient measurement, and could be used to blood glucose assay directly. Moreover, This method also possesses high selectivity and avoids the influence from the normal interference for traditional electrochemical glucose assay. In addition, the proposed sensor was further applied to the human serum samples for blood glucose assay, and the results were comparable with that given by the commercialized method. The relative standard deviation was approximately 2% indicated its high accuracy.(3) We developed a label-free electrochemical strategy for ATP detection with high sensitivity based on gold nanoparticles amplification. The introduction of ATP molecules can specifically bind with target responsive DNA(TRDNA) to form aptamer-ATP complex, and frees the anchored DNA(ADNA). The report DNA(RDNA) functionalized Au NPs can further hybridize with the unbound ADNA in proximity to the electrode surface for signal generation. [Ru(NH3)6]3+(Ru Hex), the electroactive probe, is electrostatically bound to anionic phosphates of RDNA strands, thus the detection of ATP can be achieved by chronocoulometry through the measurement of cumulative redox charge of Ru Hex. Experimental results showed that the introduction of Au NPs improved the sensitivity of this strategy significantly, and obtained a wide linear range(1 n M – 1 × 107 n M) and a low detection limit of 0.2 n M, which is more than 2 orders of magnitude lower than that of the aptasensor based on nucleic acid amplification. Furthermore, based on the same principle of sensing, by varying the aptamer and the corresponding DNA sequences, the strategy is versatile and has great potential in the construction of aptamer-based biosensors for a variety of small molecules.(4) We presented here a label-free fluorescent assay for detection of thrombin activity based on the fluorescence resonance energy transfer(FRET) between Au NPs and Enhanced green fluorescent protein(EGFP). The EGFP contains a thrombin cleavage site and a hexashisticles tag at its N-terminal, and it could be adsorbed onto the surface of Au NPs via His-Au coodination reaction, and then FRET occurs, induced the fluorescence quenched. In the presence of thrombin, it can selectively react with the cleavage site and cut the His-tag from EGFP. Therefore, the cleaved EGFPs are far away from Au NPs and maintain its fluorescence with high intensity. Based on this design, the fluorescence intensity can respond to the activity of thrombin. This assay for thrombin activity detection was achieved with a linear range of 0.1 – 1 U/m L and 0.005 – 0.05 U/m L, respectively. The minimum detectable concentration was 0.005 U/m L. Moreover, This strategy was further applied to detect hirudin which is the inhibitor of thrombin, the IC50 of hirudin was estimated to be 1.38 n M.(5) We developed a novel and highly sensitive fluorescence turn-on assay for hydrogen peroxide detection. In this assay, it was observed that fluorescence of the cationic conjugated polymer(CCP) could be efficiently quenched by Ag NPs due to strong electrostatic interactions and fluorescence resonance energy transfer. However, the Ag NPs could be oxidative etched by H2O2 to Ag+ and then the CCP could not be quenched and a fluorescence turn on signal was detected. The recovered fluorescence signal of the CCP could be directly related to the concentration of H2O2 with a linear range from 0.1 to 10 m M, and the minimum detectable concentration was 0.1 m M. In addition, quantification of H2O2 in real samples including medical disinfectant, tap water and spring water demonstrates the practicality of our assay.