Reversible and Irreversible Responses of Defect-Engineered Graphene-Based Electrolyte-Gated pH Sensors

Abstract

We have studied the role of defects in electrolyte-gated graphene mesh (GM) field-effect transistors (FETs) by introducing engineered edge defects in graphene (Gr) channels. Compared with Gr-FETs, GM-FETs were characterized as having large increments of Dirac point shift (∼30-100 mV/pH) that even sometimes exceeded the Nernst limit (59 mV/pH) by means of electrostatic gating of H(+) ions. This feature was attributed to the defect-mediated chemisorptions of H(+) ions to the graphene edge, as supported by Raman measurements and observed cycling characteristics of the GM FETs. Although the H(+) ion binding to the defects increased the device response to pH change, this binding was found to be irreversible. However, the irreversible component showed relatively fast decay, almost disappearing after 5 cycles of exposure to solutions of decreasing pH value from 8.25 to 6.55. Similar behavior could be found in the Gr-FET, but the irreversible component of the response was much smaller. Finally, after complete passivation of the defects, both Gr-FETs and GM-FETs exhibited only reversible response to pH change, with similar magnitude in the range of 6-8 mV/pH.

Recent developments in carbon-based two-dimensional materials: synthesis and modification aspects for electrochemical sensors

“…Disease-related small marker molecules like glucose [100], dopamine [87], urea [102], or environmental-related parameters such as 17β-estradiol [103], pH [104], heavy metal ions [105], or chlorine [106] have also be determined by GFETs. Selectivity can be achieved by using a differential measurement of two differently modified GFETs as it is illustrated in Fig.…”

Chemical and biological sensors based on defect-engineered graphene mesh field-effect transistors

“…To investigate the effect of defects in graphene-based FET pH sensors, electrolyte-gated graphene-FET (Gr-FET) and graphene mesh–FET (GM-FET) devices have been tested [ 32 ]. Both sensors exhibit negative Dirac point shifts upon decreases in pH.…”

“…Furthermore, the irreversible response is believed to be caused by the direct adsorption of ions onto defects, which presumably involved strong chemisorption. It has been reported that H + ions were attached so strongly to the edge defects and have only been detached after high temperature annealing [ 32 ]. Such strong interactions were rarely reversed, and thus led to passivation of the defects upon repeated exposure to acidic solutions.…”

“…For example, in the case of gas sensors based on Pd nanoparticle-decorated graphene mesh (Pd-GM), defects lowered the energy barrier during carrier injection at the Pd/graphene junction, thereby enhancing sensitivity and allowing faster response and recovery [ 31 ]. On the other hand, under a physiological environment where the graphene surface was directly exposed to electrolyte solutions, ion species were directly bound to the defect sites by means of strong chemisorption [ 32 ]. This reaction was proven to be irreversible and thus would limit its application in multiple-cycle sensor operations.…”

Полевой Эффект При Формировании Интерфейса Однослойного Графена С Водой

“…Поэтому особый интерес в последнее время вызывают интерфейсные эффекты, влияющие на электрические свойства графена [1][2][3][4][5][6][7][8]. В том числе, большое внимание направлено на создание и изучение сенсорных устройств, в которых исследуемые водные растворы находятся в интерфейсном контакте с графеном [1][2][3][4][5][6][9][10][11][12]. Интерфейсный эффект в структурах на основе выращенного в условиях вакуума четырехслойного графена, демонстрирующего дырочный тип проводимости, исследовался нами в работе [5] путем четырех контактных электрических измерений.…”