Changes in the electrical conductance of graphene field-effect transistors (GFETs) are used to perform quantitative analyses of biologically-relevant molecules such as DNA, proteins, ions and small molecules.

Chemical manipulation of estrogen receptor alpha ligand binding domain structural mobility tunes receptor lifetime and influences breast cancer therapeutic activities. Selective estrogen receptor modulators (SERMs) extend ERα cellular lifetime, accumulation, and are antagonists in the breast and agonists in the uterine epithelium and/or in bone. Selective estrogen receptor degraders (SERDs) reduce ERα cellular lifetime/accumulation and are pure antagonists. Activating somatic ESR1 mutations Y537S and D538G enable resistance to first-line endocrine therapies. SERDs have shown significant activities in ESR1 mutant setting while few SERMs have been studied. To understand whether chemical manipulation of ERα cellular lifetime and accumulation influences antagonistic activity, we synthesized a series of methylpyrollidine lasofoxifene derivatives that maintained the drug’s antagonistic activities while uniquely tuning ERα cellular accumulation. These molecules were examined alongside a panel of antiestrogens in live cell assays of ERα cellular accumulation, lifetime, SUMOylation, and transcriptional antagonism. High-resolution x-ray crystal structures of WT and Y537S ERα ligand binding domain in complex with the methylated lasofoxifene derivatives, SERMs, and SERDs show that molecules that favor a highly buried helix 12 conformation achieve the greatest transcriptional suppression activities. Together these results show that chemical reduction of ERα cellular lifetime does not necessarily correlate with transcriptional antagonism in ESR1 mutated breast cancer cells. Importantly, our approach shows how minor chemical additions modulate receptor cellular lifetime while maintaining other activities to achieve desired SERM or SERD profiles.

Graphene field-effect transistors (GFETs) present beneficial features for their application as biomolecular or chemical sensors. Due to their atomically-thin 2D dimensionality, their high electrical conductance is particularly sensitive to small changes in the distribution of charged species near the graphene surface. Taking advantage of this property, GFET sensors have been designed to report the detection or quantitation of various types of biologically-relevant molecular analytes such as nucleic acids, proteins, ions or small molecules. By analyzing data from published literature on GFET bioanalytical sensors, we have recently shown that the detection metrics of such sensors vary enormously between studies, and argued that this variance is mainly driven by disparities in the bio-recognition interface [1]. Indeed, the selectivity of GFET sensors must be engineered, typically by covering the graphene surface with biological molecules having a specific affinity for the chosen analyte (e.g. antibodies to capture the corresponding antigen, ssDNA to capture its complementary sequence). Yet, the coverage, orientation, stability and interactions between immobilized probes, blocking species and captured analytes are often not well known or controlled. In this presentation, I will discuss our efforts to understand and regulate the surface functionalization of graphene field-effect transistors. Using electrical conductance measurements and Raman spectroscopy, I will characterize the response of devices to both covalent chemistry, using aryldiazonium reagents, and non-covalent chemistry, using pyrene derivatives. I will describe our recent developments in controlling these functionalization routes, and compare their use for further bioconjugation with molecular probes for bioanalytical purposes. [1] A. Béraud, M. Sauvage, C. M. Bazán, M. Tie, A. Bencherif and D. Bouilly. Graphene Field-Effect Transistors as Bioanalytical Sensors: Design, Operation and Performance. Analyst 146, 403-428 (2021) https://doi.org/10.1039/D0AN01661F

We report on the design and assembly of liquid-gated field-effect transistor devices based on graphene ribbons, G-FETs, their functionalization with anchor groups, as well as their response to single-stranded DNA probe tethering and complementary DNA target hybridization in saline buffer solution. The probe DNA was immobilized onto the graphene surface by covalent functionalization with aryldiazonium chemistry. We characterized the electrical response of the devices before and after functionalization. DNA probe tethering and target hybridization were monitored by shifts of the charge neutrality point. Additionally, the electrical response to probe immobilization and probe-target hybridization was recorded in real-time.

Introduction: Graphene field-effect transistors (G-FETs) constitute an emerging platform for biosensing applications. Indeed, graphene is an ideal material for the detection of biomolecules: every atom of its monolayer structure is in contact with its environment, resulting in an electrical conductivity that is highly responsive to local electrostatic fluctuations from adjacent molecules. For genomic applications, most detection methods use DNA probe sequences bound to the graphene surface, in order to capture a specific target DNA sequence and detect the corresponding change in the electrical response of the sensor1 - 2. However, the effect of interactions between DNA and graphene on the electrical conductance is still not fully understood. Here, we investigate specifically the adsorption of short DNA oligomers on graphene field-effect transistors, in order to model and control the effect of such interactions in biosensing applications with G-FETs. Methods and Results: First, we fabricated G-FET sensors as follow3: Using photolithography techniques, an array of source and drain electrodes were patterned in gold on a Si wafer with a SiO2 insulator layer, as well as a common on-chip gate electrode in platinum. High-quality monolayer CVD-grown graphene was transferred onto the substrate and then etched to create 6 x 4 µm ribbons between each source-drain pair. Transfer curves (Isd vs. Vg) performed in saline buffer solution revealed a conductance minimum at the charge neutrality point of the graphene. Devices were then exposed to solutions of DNA, consisting in 22-single-stranded nucleotides (ssDNA) or double-stranded nucleotides (dsDNA) DNA oligomers diluted in 0,01X PBS buffer. Selected G-FET devices were exposed to different ssDNA concentrations during 15 min, followed by washing steps with 0,01X PBS. Electrical curves were recorded before, during and after each DNA exposure. In this presentation, we will present results showing that ssDNA exposure causes a left-shift of the charge neutrality point above a concentration threshold, and that this shift is proportional to ssDNA concentration. In addition, non-covalent adsorption of ssDNA on graphene appears to be reversible upon washing. Finally, we will discuss differences between the adsorption of dsDNA and ssDNA. Conclusion and Relevance: Our results suggest that unspecific DNA adsorption on graphene can lead to a G-FET response, which needs to be modeled, compensated and /or passivated in biosensing experiments, especially in order to achieve low detection limits for target sequences in complex biological media. References: 1. Hwang MT, Landon PB, Lee J, et al. Highly specific SNP detection using 2D graphene electronics and DNA strand displacement. Proc Natl Acad Sci. 2016;113(26):7088-7093. doi:10.1073/pnas.1603753113 2. Cai B, Wang S, Huang L, Ning Y, Zhang Z, Zhang G. Ultrasensitive Label-Free Detection of PNA À DNA Hybridization by Reduced Graphene Oxide Field-E ff ect Transistor. 2014;(3):2632-2638. doi:Doi 10.1021/Nn4063424 3. Bazan CM, Bencherif A, Sauvage M, Huliganga E, Borduas G, Bouilly D.Fabrication of Nanocarbon-Based Field-Effect Transistor Biosensors for Electronic Detection of DNA Sequences. ECS Trans. 2018;85(13):499-507. doi:10.1149/08513.0499ecst

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