Investigation of Charged Small Molecule–Aptamer Interactions with Surface Plasmon Resonance

Abstract

Investigating the interactions between small, charged molecules and aptamers using surface plasmon resonance (SPR) is limited by the inherent low response of small molecules and difficulties with nonspecific electrostatic interactions between the aptamer, analyte, and sensor surface. However, aptamers are increasingly being used in sensors for small molecule detection in critical areas like healthcare and environmental safety. The ability to probe these interactions through simple, direct SPR assays would be greatly beneficial and allow for the development of improved sensors without the need for complicated signal enhancement. However, these assays are nearly nonexistent in the current literature and are instead surpassed by sandwich or competitive binding techniques, which require additional sample preparation and reagents. In this work, we develop a method to characterize the interaction between the charged small molecule serotonin (176 Da) and an aptamer with SPR using streptavidin−biotin capture and a high-ionic-strength buffer. Additionally, other methods, such as serotonin immobilization and thiol-coupling of the aptamer, were investigated for comparison. These techniques give insight into working with small molecules and allow for quickly adapting a binding affinity assay into a direct SPR sensor.

Fast detection of Staphylococcus aureus using thiol-functionalized WS2 quantum dots and Bi2O2Se nanosheets hybrid through a fluorescence recovery mechanism

“…The smaller size and negatively charged aptamers upon binding with the WS 2 QDs make WS 2 QDs more negatively charged via electron transfer from the aptamer to the WS 2 QDs. 82 From Raman analysis, we observed that the A 1g mode is downshifted by 0.6 cm À1 from 420.4 cm À1 to 419.7 cm À1 (Fig. S5, ESI †), which confirms the electron enhancement due to aptamer functionalization.…”

“…78 The increase in electronic charge density is attributed to electron transfer from the negatively charged aptamers to the WS 2 QDs. 82 In addition to the shift, the spectral weight of the defect peak at 163.4 eV decreased to 3.0% from 15.8%, confirming the defect passivation of the WS 2 QDs by thiol-modified aptamers. The passivation of defect sites by thiol-modified aptamers increases the sulfur to tungsten ratio from 1.46 to 1.65.…”

A capacitive laser-induced graphene based aptasensor for SARS-CoV-2 detection in human saliva

“…Finally, the 5’ termini of the aptamer are labeled with a biotin-tag which may allow a correct aptamer conformation during the immobilization. Streptavidin-biotin capture technique is a common approach to immobilize aptamers in assays such as surface plasmon resonance [ 43 ]. The advantages of using streptavidin-biotin coupling to immobilize aptamers include i) a single-step immobilization which eases capture by streptavidin, ii) less constrained movement of the aptamer to avoid steric hindrances during target binding, iii) covalently linked to the end of the aptamer which allows oriented immobilization for conformation into a secondary structure, iv) streptavidin has four binding sites for biotin which enhances the attachment of aptamer to the electrode surface [ 43 , 44 ].…”

Surface plasmonic biosensors: principles, designs and applications

“…It would also be helpful to study the interaction between charged small molecules and SPR aptamers in combination with affinity measurements to improve the measurement signal of the sensors. 123 And for food safety or medical diagnostics in addition to small molecules, there are analytes of larger size and mass, such as bacteria, proteins, nucleic acids, etc . This requires direct contact with the substrate surface to achieve the measurement, and signal detection becomes more difficult.…”