Study On Biosensor For Cadmium Ion And Chemical Sensor For Organicphosphorus

Cd2+ is a environmentally and unhealthful heavy metal ions that is widely present in water, soil, plants and animals. Although some biosensor detection methods have been proposed in recent years, they still have some disadvantages such as poor sensitivity and selectivity. In order to overcome the above problem, this paper selects new recognition molecule and employs two transducer element to explore preliminarily. In addition, liquid crystal chemical sensor is used to the study on organophosphorus detection. The specific work is as follows:(1) The colorimetric biosensor for Cd2+ detection. The study selected ssDNA,which is specific for Cd2+,as recognition molecules.ssDNA attaches to the AuNPs surface by Au-N,which structures Cd2+ colorimetric probe. The sensor is fabricated on the basis of the optimal conditions,which has been further investigated for probe preparation.The detection limit is 0.5 μM, Cu2+ and Pb2+ have a slight disturbance on selectivity.(2) Liquid crystal biosensor for Cd2+ detection. Liquid crystal is used as a signal transducer and amplifier to reduce the detection limit of Cd2+. The N, N-dimethyl-N-octadecyl-3-Ammonium Propyl Trimethyl Silane (DMOAP) is used as the homeotropic orientation molecules of liquid crystal, while phosphorothioate oligonucleotides is immobilized on the glass slide surface as Cd2+ recognition molecular. Cd2+ specifically combine phosphorothioate oligonucleotides to form 2nm spherical structure, which disturbs the arrangement of liquid crystal. Polarization image will change. This detection method has high specificity and low limit. The detection limit is 0.1nM, which is far lower than that of WHO (27nM).(3) Liquid crystal chemical sensor for organophosphonates detection. In this paper,we report that the uniform perpendicular orientation of thin films(～25μm) of the nematic liquid crystal,4-biphenyl-4’-Pentyl-carbonitrile(5CB), supported on glass substrate with copper ions deposited on them.The orientation of the 5CB is driven from homeotropic to homogeneous by the competitive binding of the nitrile groups of 5CB and DIMP for the surface-immobilized copper ions in the presences of organophosphonate compounds in gas phases.This orientational transition of the LC can be observed with the naked eye by using a pair of polarizer.The sensor can respond to lOppb of DIMP and the response time is approximately 25s.The system is also demonstrated to exhibit specificity.The sensor does not respond to gaseous streams containing acetone,ethanol and water, respectively. This system does not require complex instrumentation and could provide rapid, sensitive and simple method to detect organophosphonates compare to traditional methods.