Sequestration of small molecules from aqueous solutions poses a significant and important challenge in environmental science and human health. Current methods focus on broadly sequestering all small molecules but are unable to address specific small molecules of interest. Additionally, these procedures require large amounts of resources, such as electricity and pressure. We propose to address this challenge through the use of DNA aptamer-functionalized ultrafiltration membranes. To demonstrate this approach, we developed an aptamer-functionalized membrane that sequesters and removes the small-molecule contaminant bisphenol A (BPA) from water. We show that BPA is depleted and that the membranes can be regenerated for multiple uses, which can allow for recovery of the small molecule when desired. Aptamers can be selected for a wide variety of target small molecules, making this approach highly generalizable beyond our initial demonstration. Together, this research offers a promising solution to improving the efficacy of small molecule removal and recovery from aqueous matrices.

Small-molecule toxins pose a significant threat to human health and the environment, and their removal is made challenging by their low molecular weight. Aptamers show promise as affinity reagents for binding these toxins, and recently, aptamers have been utilized for both sensing and remediation applications. We found that functionalization of ultrafiltration membranes with aptamers provides a convenient scaffold for toxin sequestration, but our initial efforts in this area were limited by low functionalization efficiencies and the ability to only capture a single target molecule. Herein, we describe detailed optimization of our aptamer-functionalized ultrafiltration membrane system and subsequent use for simultaneous removal of multiple small-molecule toxins. We examine multiple critical components involved in fabricating and functionalizing the membranes, including PEG polymer molecular weight for membrane fabrication, grafting conditions for pMAA attachment, and coupling reagents for aptamer functionalization. This screening enabled us to identify a set of unique conditions in which we were able to achieve high flux, near quantitative yield for DNA attachment, and effective overall depletion of both toxins and bacterial cells. Furthermore, we demonstrate the attachment of multiple aptamers and subsequent parallel removal of atrazine, bisphenol A, and microcystin-LR in a complex lake water matrix. Our rigorous evaluation resulted in depletion of multiple small-molecule toxins, contaminants, and microorganisms, demonstrating the potential of aptamer-functionalized membranes as point-of-use decontamination systems.

Small molecule contaminants pose a significant threat to the environment and human health.

Aptamer-functionalized membranes offer a promising platform for toxin removal, but regeneration of binding capacity requires heat and washing. Moreover, bound molecules can be eluted, resulting in recontamination. Here we report the tandem use of aptamers and enzymes to trap and degrade small-molecule contaminants, resulting in an autonomously self-regenerating purification system.

Fluorophore bioconjugation to proteins, nucleic acids, and other important molecules can provide a powerful approach to sensing, imaging, and quantifying chemical and biological processes. One of the most prevalent methods for fluorophore attachment is through the formation of amide bonds, which are often facilitated by coupling agents to activate carboxylic acid moieties for subsequent nucleophilic attack by amines. 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM) is among the most popular of these coupling agents for bioconjugation due to its ability to facilitate amide bond formation in water. After observing quenching of 5-fluoresceinamine (5-FAM)-conjugated oligonucleotides in the presence of DMTMM, we sought to evaluate the magnitude and scope of this challenge by surveying the effect of DMTMM on a range of fluorescent dyes. A higher quenching effect was consistently observed for xanthene dyes compared to that for cyanine dyes. Further analysis of the impact of DMTMM on FAM shows that quenching occurs independently of whether the dye is free in solution or attached to an oligonucleotide or antibody. Furthermore, we found that FAM-conjugated DNA was unable to recover its fluorescence after the removal of DMTMM, and UV–vis and NMR analyses suggest the formation of new products, such as an adduct formed between FAM and the dimethoxytriazine of DMTMM. As such, DMTMM at high concentrations is not recommended for coupling reactions where targets are fluorescently labeled. This research serves as a word of caution to those utilizing xanthene-containing fluorophores in bioconjugation reactions involving DMTMM.

Fluorophore bioconjugation to proteins, nucleic acids, and other important molecules can provide a powerful approach to sensing, imaging, and quantifying chemical and biological processes. One of the most prevalent methods for fluorophore attachment is through the formation of amide bonds, which are often facilitated by coupling agents to activate carboxylic acid moieties for subsequent nucleophilic attack by amines. DMTMM is among the most popular of these coupling agents for bioconjugation due to its ability to facilitate amide bond formation in water. After observing quenching of 5-fluoresceinamine (FAM)-conjugated oligonucleotides in the presence of DMTMM, we sought to evaluate the magnitude and scope of this challenge by surveying the effect of DMTMM on a range of fluorescent dyes. A higher quenching effect was consistently observed for xanthene dyes compared to cyanine dyes. Further analysis of the impact of DMTMM on FAM shows that quenching occurs independently of whether the dye is free in solution or attached to a DNA oligonucleotide or antibody. Furthermore, we found that FAM-conjugated DNA was unable to recover its fluorescence after the removal of DMTMM and UV-Vis and NMR analysis suggests the formation of new products. However, further studies are needed to elucidate the specific analogues being formed. This research serves as a word of caution to those utilizing xanthene-containing fluorophores in bioconjugation reactions involving DMTMM.

Aptamer-functionalized membranes are a promising platform for toxin removal and small-molecule sequestration. However, this function can be compromised when the aptamer binding sites become saturated, and regeneration of the membrane requires heat and multiple washes to restore the aptamer binding capabilities. Additionally, bound molecules can be eluted into water sources, resulting in recontamination. Herein, we address this challenge by creating autonomously self-regenerating membranes through the tandem use of aptamers and enzymes to trap and degrade small-molecule contaminants. To demonstrate this approach, we developed an enzyme–aptamer-functionalized membrane that sequesters and degrades the small-molecule contaminant bisphenol A (BPA) from water. We show that BPA is not only depleted but also degraded, as the membrane is able to be reused for multiple cycles without the need for heat or washing to restore function. Given the large number of reported DNA aptamers for small molecule analytes, we envision that this research will provide a broadly applicable platform for the removal of waterborne contaminants.

What would you suggest to an international student culturally very different from their lab to help the principal investigator and current members understand their culture? For example, some behaviors can be misinterpreted if people are not familiar with the culture. What is the best way to help people understand without changing who we are?—Anonymous grad student Studying in another country can catalyze a rich exchange that benefits you and the students and faculty that you work with. However, blending your cultural traditions with those of your host country can be challenging. To bring insight to this topic, Misael Romero-Reyes, a fourth-year graduate student in my lab who is originally from Mexico, has joined me this month. Misael is a leader at Emory University, where he has been working to advance diversity and inclusion and create opportunities for international students to build support networks and community. I’ll let Misael take it