Diego Pallarola

Electronic tongue for simultaneous detection of endotoxins and other contaminants of microbiological origin.

Endotoxins, also referred to as pyrogens, are lipopolysaccharides (LPS) present in the outer membrane of Gram-negative bacteria, and represent one of the most dangerous microbiological contaminants in water for hemodialysis and intravenous infusion. A method is presented for the simultaneous detection of endotoxins and other bacterial lysis contaminating species in purified water for parenteral formulations. The technique used is electrochemical impedance spectroscopy, with data interpretation using principal component analysis (PCA), cluster analysis (CA), and multivariate discriminant analysis (MDA). Two types of electrode surfaces were modified with LPS recognition agents: (i) a 37 amino acids fragment of a 18 kDa cationic antimicrobial protein (CAP18F) that has LPS binding activity; (ii) the highly selective endotoxin neutralizing protein (ENP). Statistical multivariate analysis of the impedance spectral data allowed the detection of endotoxin at, and below, the threshold pharmaceutical regulatory level. Discrimination of LPS from samples containing proteins, nucleic acids, phospholipids or their mixtures was achieved. These results open a new route to a practical instrumental method capable of detecting and discriminating LPS from other potential pro-inflammatory species of microbiological origin, such as nucleic acids.

Redox-active concanavalin A: synthesis, characterization, and recognition-driven assembly of interfacial architectures for bioelectronic applications.

The convergence of chemistry, biology, and materials science has paved the way to the emergence of hybrid nanobuilding blocks that incorporate the highly selective recognition properties of biomolecules, with the tailorable functional capabilities of inorganic molecules. In this work, we describe for the first time the decoration of concanavalin A (Con A), a protein with the ability to recognize sugars and form glycoconjugates, with Os(II) redox-active complexes. This strategy enabled the construction of electroactive biosupramolecular materials whose redox potentials could be easily modulated through the facile molecular modification of the electroactive inorganic complexes. Small-angle X-ray scattering (SAXS), steady-state fluorescence, surface plasmon resonance (SPR) spectroscopy, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS), and differential-pulsed (DPV) and cyclic voltammetry (CV) were used to characterize the structural and functional features of the synthesized biohybrid building blocks as well as their respective supramolecular assemblies built up on gold electrodes. By harnessing the electroactive and carbohydrate-recognition properties of these tailor-made biohybrid building blocks, we were able to integrate glucose oxidase (GOx) onto gold electrodes via sugar-lectin interactions. The redox activity of the Os-modified Con A interlayer allowed the electronic connection between the multilayered GOx assemblies and the metal electrode as evidenced by the well-defined bioelectrocatalytic response exhibited by the biomolecular assemblies in the presence of the glucose in solution. We consider that this approach based on the spontaneous formation of redox-active biosupramolecular assemblies driven by recognition processes can be of practical relevance for the facile design of biosensors, as well as for the construction of new multifunctional bioelectrochemical systems.

Recognition-driven layer-by-layer construction of multiprotein assemblies on surfaces: a biomolecular toolkit for building up chemoresponsive bioelectrochemical interfaces

The development of soft bioelectronic interfaces with accurate compositional and topological control of the supramolecular architecture attracts intense interest in the fast-growing field of bioelectronics and biosensing. The present study explores the recognition-driven layer-by-layer assembly of glycoenzymes onto electrode surfaces. The design of the multi-protein interfacial architecture is based on the multivalent supramolecular carbohydrate-lectin interactions between redox glycoproteins and concanavalin A (Con A) derivatives. Specifically, [Os(bpy)(2)Clpy](2+)-tagged Con A (Os-Con A) and native Con A were used to direct the assembly of horseradish peroxidase (HRP) and glucose oxidase (GOx) in a stepwise topologically controlled procedure. In our designed configuration, GOx acts as the biorecognition element to glucose stimulus, while HRP acts as the transducing element. Surface plasmon resonance (SPR) spectroscopy and quartz crystal microbalance with dissipation (QCM-D) results are combined to give a close representation of the protein surface coverage and the content of water in the protein assembly. The characterization is complemented with in situ atomic force microscopy (AFM) to give a topographical description of the layers assemblage. Electrochemical (EC) techniques were used to characterize the functional features of the spontaneously self-assembled biohybrid architecture, showing that the whole system presents efficient electron transfer and mass transport processes being able to transform micromolar glucose concentration into electrical information. In this way the combination of the electroactive and nonelectroactive Con A provides an efficient strategy to control the position and composition of the protein layers via recognition-driven processes, which defines its sensitivity toward glucose. Furthermore, the incorporation of dextran as a permeable interlayer able to bind Con A promotes the physical separation of the biochemical and transducing processes, thus enhancing the magnitude of the bioelectrochemical signal. We consider that these results are relevant for the nanoconstruction of functional biointerfaces provided that our experimental evidence reveals the possibility of locally addressing recognition, transduction and amplification elements in interfacial ensembles via LbL recognition-driven processes.

Surfactant-Assisted Lipopolysaccharide Conjugation Employing a Cyanopyridinium Agent and Its Application to a Competitive Assay

The activation of a lipopolysaccharide (LPS) with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) in the presence of a surfactant allows an efficient conjugation with dansyl hydrazine or horseradish peroxidase (HRP) in an aqueous medium maintaining its biological activity. In order to promote the reaction a series of amphiphilic compounds were tested, sodium deoxycholate being the most suitable. The method presents several advantages: it is carried out in a mild environment, good conjugation ratios are obtained, it is suitable for any label bearing amino, hydrazine, or hydrazide groups, and the LPS endotoxic and HRP enzymatic activities are preserved. The HRP conjugate is applied in an amperometric competitive assay for the detection of lipopolysaccharides in an electrode array combined with a multipotentiostat able to carry out simultaneous determinations. The system is able to detect samples in concentrations as low as 100 pg mL(-1) of LPS.

Facile Glycoenzyme Wiring to Electrode Supports by Redox-Active Biosupramolecular Glue

The integration of redox glycoproteins on conductive supports plays a pivotal role in the successful design of bioelectronic platforms, including, among others, biosensors or biofuel cells. [1] This is strongly related to the ability to control the interfacial architecture and the quality of the association between the enzyme and the electrode surface. This aspect is particularly important for amperometric biosensors by virtue of the complex interplay between the reactions that give rise to the electronic signal and the assemblage of the biorecognition elements onto the solid support. [2] Apart from retaining the biological activity of the enzyme, the immobilisation procedure must guarantee the accessibility of its active site to the target analyte and other molecules involved in the biorecognition event. It is known that many immobilization methodologies can induce conformational changes in the enzyme, which could be accompanied by a significant loss of enzymatic activity. [3] Within this framework, recognition-directed biosupramolecular assembly emerged as an interesting and attractive alternative due to its simplicity and versatility, without introducing chemical modifications to the enzyme. This non-covalent approach, also known as bioaffinity layering, is based on the remarkable selectivity of the interaction between the constituting

Self-limited self-assembly of nanoparticles into supraparticles: towards supramolecular colloidal materials by design

For quite a while, scientists have resorted to colloidal synthesis to mimic complex structural and functional materials found in Nature. In particular, within the past few years, the synthesis of suprastructures with novel properties that emerge from the coupling of diverse nanoscale functional units has defined new boundaries in materials science. In this mini-review, we survey the most recent and outstanding achievements on the rational design of supraparticles based on the self-limited self-assembly of nanoparticles, and their application in fields like biology, medicine and energy.

Two Efficient Methods for the Conjugation of Smooth-Form Lipopolysaccharides with Probes Bearing Hydrazine or Amino Groups. I. LPS Activation with Cyanogen Bromide

This chapter presents a conjugation method for coupling probes bearing hydrazine or primary amino groups to a smooth(S)-form lipopolysaccharide (LPS). LPS is modified by the activation of the hydroxyl groups present in its O-antigen moiety with cyanogen bromide in aqueous acetone. The method yields conjugates with good labeling ratios, preserving the endotoxic activity of the lipid A moiety. Conjugation of smooth-form LPS from Salmonella enterica sv. Minnesota with dansyl hydrazine and horseradish -peroxidase yields labeling ratios above 300 nmol dansyl per mg LPS, with nearly no loss of the original endotoxin activity. In the case of horseradish peroxidase, introducing a spacer, a ratio of 28 nmol HRP per mg LPS is obtained, preserving 65% of the original endotoxic activity.

Two efficient methods for the conjugation of smooth-form lipopolysaccharides with probes bearing hydrazine or amino groups. II. LPS activation with a cyanopyridinium agent.

This chapter presents a conjugation method for coupling probes bearing hydrazine or primary amino groups to a lipopolysaccharide (LPS). LPS is modified by the activation of the hydroxyl groups present in its O-antigen moiety with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP). The method yields conjugates with good labeling ratios, preserving the endotoxic activity of the lipid A moiety. Conjugation of smooth-form LPS from Salmonella enterica sv. Minnesota with dansyl hydrazine and horseradish peroxidase yields labeling ratios above 110 nmol dansyl/mg LPS, with nearly no loss of the original endotoxic activity. In the case of horseradish peroxidase, introducing a spacer, a ratio of 29 nmol HRP/mg LPS was obtained, preserving 65% of the original endotoxic activity and an enzymatic activity of 120 U/mg.