We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dualphase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, 3.7 × 10 −44 cm 2 , for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DMparticle mass of 49 GeV/c 2 at 90% confidence level.PACS numbers: 95.35.+d, 95.55.Vj

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In this paper, we describe the synthesis of a novel copper ion hapten using the copper mercaptide of penicillenic acid (CMPA) derived from penicillin. Results from tests with immune rabbits indicate that: (i) A new antigen synthesized with CMPA has good stability and is safe for immunizing animals with no toxic phenomena being found in animal experiments; (ii) the immunogenic antigen (CMPA-BSA) can stimulate the immune system to produce specific antibodies with high titrations, up to 150000; and (iii) antibodies in antisera showed higher affinity to OVA-GSH-CuCl than OVA-GSH, which indicates that the antibodies have specific affinity towards copper ions. These results confirm that the novel hapten and relevant antigen for copper ion have been successfully synthesized, giving progress towards an immunoassay for copper ions in environmental and food samples. Heavy metals are a class of persistent toxic contaminants and residues found at various levels in the environment and in agricultural and industrial products [1]. Unlike carbon-based contaminants that can be completely degraded to relatively harmless products, metal ions can be transformed in only a limited number of ways through chemical or biological remediation processes [2]. What is worse, through biomagnifications, heavy metal ions existing in the environment can invade the human body and remain there for a long time, posing a serious threat to human health [3].Copper is an essential element of some metalloenzymes necessary for the normal course of biochemical processes but, like other heavy metals, it is toxic at high concentration [4,5]. All of these factors pose potential risks for the environment and human health [6] and therefore copper and other heavy metals must be monitored and identified in the environment. The traditional technologies for detecting heavy metals are instrument-based measurements such as atomic absorption spectrometry [7], inductively coupled plasma spectroscopy (ICP-AES and ICP-MS) [8] and stripping voltammetry [9]. Although these conventional instruments accurately detect the amount of metal in an individual sample, they all require expensive laboratory equipment in a centralized facility and sample turnaround is slow. In addition, instrumental analyses provide no information about the metal oxidation state.In this case, immunoassays based on the affinity and specificity of an antigen-antibody reaction offer an alternative approach in the field of metal ion measurement. Com-