Detection of Glial Fibrillary Acidic Protein in Patient Plasma Using On-Chip Graphene Field-Effect Biosensors, in Comparison with ELISA and Single-Molecule Array

Abstract

Glial fibrillary acidic protein (GFAP) is a discriminative blood biomarker for many neurological diseases, such as traumatic brain injury. Detection of GFAP in buffer solutions using biosensors has been demonstrated, but accurate quantification of GFAP in patient samples has not been reported, yet in urgent need. Herein, we demonstrate a robust on-chip graphene field-effect transistor (GFET) biosensing method for sensitive and ultrafast detection of GFAP in patient plasma. Patients with moderate–severe traumatic brain injuries, defined by the Mayo classification, are recruited to provide plasma samples. The binding of target GFAP with the specific antibodies that are conjugated on a monolayer GFET device triggers the shift of its Dirac point, and this signal change is correlated with the GFAP concentration in the patient plasma. The limit of detection (LOD) values of 20 fg/mL (400 aM) in buffer solution and 231 fg/mL (4 fM) in patient plasma have been achieved using this approach. In parallel, for the first time, we compare our results to the state-of-the-art single-molecule array (Simoa) technology and the classic enzyme-linked immunosorbent assay (ELISA) for reference. The GFET biosensor shows competitive LOD to Simoa (1.18 pg/mL) and faster sample-to-result time (<15 min), and also it is cheaper and more user-friendly. In comparison to ELISA, GFET offers advantages of total detection time, detection sensitivity, and simplicity. This GFET biosensing platform holds high promise for the point-of-care diagnosis and monitoring of traumatic brain injury in GP surgeries and patient homes.

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“…2,23 Moreover, after PBASE functionalisation, the G band exhibits a shoulder at 1628 cm −1 , which is attributed to pyrene group resonance, proving that PBASE is adsorbed onto the graphene surface. [21][22][23] Finally, an increase in the I 2D /I G ratio after functionalisation has been observed as reported in previous works (Fig. S1 †).…”

“…This demonstrates that, when the adsorption of PBASE on CVD-G is controlled, a flatter surface is formed as a result of a uniform and dense packing of the pyrene core on the graphene basal plane. 21 An increase in the surface roughness after PBASE functionalisation, frequently reported in previous works, 2,22 is instead symptomatic of PBASE aggregation on the surface and, therefore, non-efficient functionalisation. By comparing the lock-in phase micrographs (Fig.…”

“…S1 †). 2,21,22 PBASE adsorption on graphene can be further monitored by observing the N 1s core level at XPS, which increases from 0.45 to 0.75 at% upon functionalisation (Fig. 3B).…”

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“…GFET biosensors have been demonstrated for the detection of SARS-CoV-2 viruses, 13 neutralizing antibodies, 13,16,17 and other human-infectious viruses such as Zika, 18 avian influenza, 19,20 Ebola, 21 and the human immunodeficiency virus (HIV). 22 They have also been used for the detection of a wide range of biomolecules, including proteins, 23,24 DNA, [25][26][27] small molecules, [28][29][30] other disease biomarkers. [31][32][33] Nevertheless, there are practical limitations that prevent their broad implementation in real applications.…”

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“… 4 However, GFAP levels are too low for routine detection by commonly used protein diagnostic tests such as ELISA, and more sensitive methods for its identification are needed. 5 …”