Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • According to the data from our

    2018-10-26

    According to the data from our control experiments, which were measured from devices without a passivation layer, the doping effect dominated the sensing mechanism (Fig. 6c) due to the increased conductivity with the accumulation of more positive charges at the device. In our group, Chen et al. [7] investigated the rGO FET sensing properties based on the doping effect with a lower detection limit of 25nM. In addition, An et al. reported a gated FET-type flexible graphene aptasensor with high sensitivity and selectivity for Hg2+, whose lower detection limit was 10pM [3]. However, without a passivation layer, the sensing signal could be disturbed by free ions as charge carriers across electrodes (Fig. 6c). With a passivation layer, interferences can be minimized and the conductivity change of the rGO/Al2O3/DNA sensor is the direct electrostatic gating effect from the accumulation of the positively charged Hg2+ on the gate (Fig. 6d). With the ultra-thin 1nm Al2O3 deposition, the device may be covered only by discontinuous Al2O3 islands. Partial coverage of the few cycles of ALD deposition (less than 10) has been observed in other work [30]. In that case, the 1nm Al2O3 layer could only be functional to passivate the rGO surface, but not to fully protect rGO from the adsorption of free metal ions; therefore, the 1nm-thick layer deposition led to a lower sensitivity. Our results show that the performance of the sensor highly depends on the thickness of the passivation layer, suggesting that the reported sensor performance could be further enhanced by simply depositing Al2O3 passivation layers with varying thicknesses and controlling the uniformity of passivation films. For example, even lower detection limits potentially could be achieved by adjusting the thickness of Al2O3 properly to enhance the gate electrical effect on the sensor device. Generally, the intrinsic electrical properties of rGO combined with the advanced gate dielectrics (Al2O3) may open a new route to design high-performance rGO FET sensor devices.
    Conclusions In summary, we fabricated an rGO FET water sensor platform with a passivation layer (Al2O3), which showed a highly sensitive and selective response to various mercury buy Z-IETD-FMK concentrations. With a passivation layer to protect the electrical stability of the devices, the sensor demonstrated a clear gate effect mechanism, which could help us to improve sensing performance. Probe DNA was uniformly immobilized onto the Au NP surfaces through Au-thiol interactions, and this method has better performance than other chemical methods due to the uniform distribution of Au NPs on the devices. The sensing capability of the sensor was demonstrated by a fast response (several seconds) and a significantly lower detection limit (1nM). Moreover, the sensor showed high selectivity in mixed solutions. Our sensor platform offers a promising route for large-scale, low-cost, real-time, and high-performance chemical sensing and biosensing applications.
    Conflict of interest
    Acknowledgments Financial support for this work was provided by the U.S. National Science Foundation through the Industry/University Cooperative Research Center on Water Equipment & Policy located at the University of Wisconsin–Milwaukee and Marquette University (IIP-0968887), a fundamental research grant (IIP-1128158), a Partnership for Innovation (PFI) grant (IIP-1434059), and University of Wisconsin–Milwaukee Research Foundation Bradley Catalyst Grant. The e-beam lithography was performed at the Center for Nanoscale Materials of Argonne National Laboratory, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. CNM 32436. The authors thank Dr. H.A. Owen for technical support with SEM analyses.
    Introduction Oxalic acid is a strong acid (pKa1=1.23 and pKa2=4.19) simple hydrophilic molecule [log KO/W=−0.7] having high solubility in water and is present in spinach, cabbage, broccoli, mushrooms and Brussels sprouts. Oxalic acid (OA) is widely distributed in various organisms, fungi, plants and animals. High levels of OA remove calcium from blood that can cause severe disturbance in the activity of heart and neural system. It has been found that OA may cause digestive tract irritation and kidney damage; hence there is an increasing demand for its determination in biofluids [1,2]. Excess of oxalic acid may result in the formation of oxalate stones in bladder and kidneys (calcium oxalate and calcium phosphate). Calcium oxalate stone formation may be caused by high level of calcium, and high oxalate excretion. Oxalic acid converts into oxalate in the body, and hence prevents the sedimentation of calcium in bones by sticking to it. In other words, it causes calcium excretion, and hence deficiency. Therefore, the need to design an electrochemical platform in the form of a strip sensor, for detection of OA can hardly be stressed.