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Complexometric Titration: Ligands00:43

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Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...
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In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
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Divalent Cation Dependence Enhances Dopamine Aptamer Biosensing.

Nako Nakatsuka1,2, John M Abendroth1,2, Kyung-Ae Yang3

  • 1Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States.

ACS Applied Materials & Interfaces
|January 7, 2021
PubMed
Summary
This summary is machine-generated.

Dopamine aptamer sensors show enhanced performance in physiological conditions due to divalent cations like Mg2+ and Ca2+. This cation interaction is specific to the new dopamine aptamer, not serotonin or older dopamine aptamers.

Keywords:
Ca2+Debye lengthMg2+circular dichroism spectroscopyfield-effect transistorneurotransmitteroligonucleotidesserotonin

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Area of Science:

  • Biomedical Engineering
  • Analytical Chemistry
  • Molecular Biology

Background:

  • Aptamers are oligonucleotide receptors that change conformation upon target binding, enabling electronic biosensing.
  • Field-effect transistor (FET) biosensors are sensitive to ionic conditions due to aptamer backbone charge.
  • Evaluating biosensor performance under application-relevant ionic conditions is crucial.

Purpose of the Study:

  • To investigate the impact of physiological ion concentrations on aptamer FET-sensor performance.
  • To characterize the role of divalent cations (Mg2+, Ca2+) in dopamine and serotonin aptamer-based biosensing.
  • To elucidate the sensing mechanisms influenced by ionic environments.

Main Methods:

  • Fabrication and testing of aptamer-functionalized field-effect transistor (FET) sensors.
  • Evaluation of sensor response to dopamine and serotonin under varying ionic strengths, including artificial cerebrospinal fluid.
  • Circular dichroism spectroscopy to analyze aptamer secondary structure changes.
  • Thioflavin T displacement assays to confirm target-binding interactions.

Main Results:

  • Physiological concentrations of Mg2+ and Ca2+ significantly potentiated dopamine detection by a new dopamine aptamer FET-sensor.
  • This potentiation was not observed with a serotonin aptamer or a previously reported dopamine aptamer.
  • Circular dichroism and Thioflavin T assays indicated Mg2+- and Ca2+-induced structural changes specific to the new dopamine aptamer, suggesting allosteric binding.

Conclusions:

  • Divalent cations play a critical role in the performance of specific aptamer-based biosensors, such as the new dopamine aptamer.
  • Allosteric interactions between divalent cations and the target molecule (dopamine) influence aptamer conformation and sensor signal.
  • Testing aptamer sensors in physiologically relevant ionic environments is essential for identifying optimal candidates and understanding sensing mechanisms.