Lumped-Capacitive Modeling and Sensing Characteristics of an Electrolyte-Gated FET Biosensor for the Detection of the Peanut Allergen

Sensing Characteristics of SARS-CoV-2 Spike Protein Using Aptamer-Functionalized Si-Based Electrolyte-Gated Field-Effect Transistor (EGT)

“…To further understand the sensing responses of EGT in detecting the aptamer–SC2 conjugate, a lumped-capacitive model with the presence of a dipole layer and a capacitive component was employed [ 19 , 36 , 37 ]. The binding factor α, defined as the ratio of the aptamer sites bound with the SC2 molecules to the total aptamer sites, can be expressed as [ 33 , 36 , 38 ] where N AP_SC2 is the density of the aptamer–SC2 conjugates, N AP is the density of total immobilized aptamers, K is related to the dissociation constant of the aptamer–SC2 binding, and n is a slope factor that indicates the cooperativity of SC2 binding.…”

“…After introducing SC2 to the aptamer-functionalized surface, it generates an effective dipole moment ( V DP_EFF ) and an effective capacitance ( C FN_EFF ). V DP_EFF can be expressed as follows [ 20 , 36 , 37 ]: where P DP is the perpendicular component of the dipole moment, ε DP is the permittivity of the dipole layer, and V DP_GT is the dipole potentials at the gate electrode. V DP_EFF is mainly determined from the gate electrode since the gate area is ~5000 times larger than the channel area in the fabricated EGT device.…”

“…C FN_EFF is related to the biomaterials on the channel and can be expressed as follows [ 36 ]: where C SC2_CH and C AP_CH are the SC2 and aptamer capacitances per unit area at the channel.…”

“…By utilizing equations (3), the binding factor α can be calculated as α = [SC2] 0.2 /(4.7 × 10 −2 + [SC2] 0.2 ) with K = 4.7 × 10 −2 and n = 0.2. A lower K value of the aptamer reaction, compared to the previous protein detection ( K = 1.84 × 10 −3 ), indicates that the aptamer conjugate is more prone to dissociation than the peanut protein conjugates [ 36 ]. In Figure 6 b, the extracted C FN_EFF is fitted as C FN_EFF = 1.37 × 10 −8 − 9.4 × 10 −12 × [SC2] −0.2 ≈ 1.37 × 10 −8 using the extracted K and n values.…”

“…where PDP is the perpendicular component of the dipole moment, εDP is the permittivity To further understand the sensing responses of EGT in detecting the aptamer-SC2 conjugate, a lumped-capacitive model with the presence of a dipole layer and a capacitive component was employed [19,36,37]. The binding factor α, defined as the ratio of the aptamer sites bound with the SC2 molecules to the total aptamer sites, can be expressed as [33,36,38]…”