Roberto de la Rica

Enzyme-responsive nanoparticles for drug release and diagnostics ☆

Enzymes are key components of the bionanotechnology toolbox that possess exceptional biorecognition capabilities and outstanding catalytic properties. When combined with the unique physical properties of nanomaterials, the resulting enzyme-responsive nanoparticles can be designed to perform functions efficiently and with high specificity for the triggering stimulus. This powerful concept has been successfully applied to the fabrication of drug delivery schemes where the tissue of interest is targeted via release of cargo triggered by the biocatalytic action of an enzyme. Moreover, the chemical transformation of the carrier by the enzyme can also generate therapeutic molecules, therefore paving the way to design multimodal nanomedicines with synergistic effects. Dysregulation of enzymatic activity has been observed in a number of severe pathological conditions, and this observation is useful not only to program drug delivery in vivo but also to fabricate ultrasensitive sensors for diagnosing these diseases. In this review, several enzyme-responsive nanomaterials such as polymer-based nanoparticles, liposomes, gold nanoparticles and quantum dots are introduced, and the modulation of their physicochemical properties by enzymatic activity emphasized. When known, toxicological issues related to the utilization nanomaterials are highlighted. Key examples of enzyme-responsive nanomaterials for drug delivery and diagnostics are presented, classified by the type of effector biomolecule, including hydrolases such as proteases, lipases and glycosidases, and oxidoreductases.

Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth

Lowering the limit of detection is key to the design of sensors needed for food safety regulations, environmental policies and the diagnosis of severe diseases. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10(-18) g ml(-1) (4 × 10(-20) M) in whole serum.

Plasmonic ELISA for the detection of analytes at ultralow concentrations with the naked eye

This protocol describes a signal-generation mechanism for the naked-eye detection of analytes at low concentrations with ELISA. The key step is to generate solutions of desired tonality by growing gold nanoparticles with a particular state of aggregation. This is accomplished by linking the growth of gold nanoparticles with the biocatalytic cycle of the enzyme label. The protocol adapts a conventional ELISA procedure with catalase-labeled antibodies. The enzyme consumes hydrogen peroxide, and then gold (III) ions are added to generate gold nanoparticles. The concentration of hydrogen peroxide dictates the state of aggregation of gold nanoparticles. This allows for the naked-eye detection of analytes by observing the generation of blue- or red-colored gold nanoparticle solutions. When coupled with conventional ELISA, this signal-generation procedure allows for the naked-eye detection of analytes within 1 h.

Label-Free Pathogen Detection with Sensor Chips Assembled from Peptide Nanotubes

A robust viral sensor was developed by bridging a pair of gold electrodes with antibody-coated peptide nanotubes. The nanotubes concentrated the target virus on their surface by molecular recognition between the antibody and the virus (see picture). The nanotubes fit perfectly within the electric field line distribution to enable the extremely sensitive impedimetric detection of viral particles.

Urease as a nanoreactor for growing crystalline ZnO nanoshells at room temperature.

Reactor core: Hybrid core–shell urease–ZnO nanostructures have been synthesized (see picture). The crystallization takes place under mild biological conditions, thus ensuring its easy implementation in other room-temperature syntheses of oxide semiconductor materials.

Multivalent nanoparticle networks as ultrasensitive enzyme sensors

As few as 23 enzyme molecules could be detected on the basis of the dispersion of Au nanoparticles in a model bioassay whose sensitivity was boosted by the interplay between multivalent and monovalent supramolecular interactions: a diferrocenyl ligand (red) caused the assembly of nanoparticle clusters; upon its oxidation, a competing monovalent guest molecule (blue) favored the formation of monovalent interactions for more efficient

Label-Free Cancer Cell Detection with Impedimetric Transducers

While cancer is still an implacable disease, many cancers can be cured if they are diagnosed in an early stage. Recently, it was reported that the transformation from normal cells to cancer cells can change their mechanoelastic properties to become softer and more deformable. If some cancer cells are more deformable, then a progressive increase of the volume of softer cancer cells should be induced as an abrupt change in osmolarity is applied. On the basis of this hypothesis, we developed a sensor that can electronically monitor the volume increase of cancer cells under hyposmotic pressure. By this methodology, K:Molv NIH 3T3 cells, 786-O human kidney carcinoma cells, and MPSC-1 ovarian cancer cells were successfully detected within 30 min using on the order of 10 cells. These cancer cells could be detected with the same sensitivity even in the presence of a vast excess of the respective noncancerous cells [NIH 3T3 cells, human embryonic kidney (HEK) 293 cells, ovarian surface epithelial (OSE) cells]. Since the proposed impedimetric sensor could be useful for detecting cancer cells fast and reliably, it could be further implemented in the screening of large populations of tissue samples and the detection of circulating tumor cells for point-of-care applications.

Biomimetic Crystallization of Ag2S Nanoclusters in Nanopore Assemblies

Self-organized nanocrystal architectures with subnanometric spatial resolution were obtained by mimicking the biological crystal growth. The key step of this facile, one-pot, biomimetic route is to induce the self-assembly of the artificial nanopore cucurbit[7]uril with metal ions, which generates supramolecular aggregates that recreate the physicochemical environment of biomineralization processes. The approach holds great promise for the fabrication of nanocrystal superstructures of functional materials, useful in optics, electronics, and catalysis.

Supramolecular Au nanoparticle assemblies as optical probes for enzyme-linked immunoassays

A novel enzyme-linked immunoassay with nanoparticle assemblies as optical probes is presented. The macrocycle cucurbit[7]uril assembles gold nanoparticles, and the enzymatic generation of ammonium by urease as the label of the immunoassay disperses the probes to yield variations of plasmon absorbance that are proportional to the target protein concentration.

Bioinspired target-specific crystallization on peptide nanotubes for ultrasensitive Pb Ion detection

An ultralow concentration of Pb ions is detected by a sensor integrating a peptide nanotube detection platform with a smart peptide function that specifically metalizes the target ion. As the PbII-binding peptide on the nanotube, which bridges two electrodes, templates Pb nanowires, a resistor appears in the circuit, and conductance is detected as the signal for PbII.