In this work we summarize the main results obtained with the portable surface plasmon resonance (SPR) device
developed in our group (commercialised by SENSIA, SL, Spain), highlighting its applicability for the real-time detection
of extremely low concentrations of toxic pesticides in environmental water samples. In addition, we show applications in
clinical diagnosis as, on the one hand, the real-time and label-free detection of DNA hybridization and single point
mutations at the gene BRCA-1, related to the predisposition in women to develop an inherited breast cancer and, on the
other hand, the analysis of protein biomarkers in biological samples (urine, serum) for early detection of diseases.
Despite the large number of applications already proven, the SPR technology has two main drawbacks: (i) not enough
sensitivity for some specific applications (where pM-fM or single-molecule detection are needed) (ii) low multiplexing
capabilities. In order solve such drawbacks, we work in several alternative configurations as the Magneto-optical Surface
Plasmon Resonance sensor (MOSPR) based on a combination of magnetooptical and ferromagnetic materials, to
improve the SPR sensitivity, or the Localized Surface Plasmon Resonance (LSPR) based on nanostructures
(nanoparticles, nanoholes,...), for higher multiplexing capabilities.
In order to solve the drawbacks of sensitivity and portability in optical biosensors we have developed ultrasensitive and miniaturized photonic silicon sensors able to be integrated in a "lab-on-a-chip" microsystem platform. The sensors are integrated Mach-Zehnder interferometers based on TIR optical waveguides (Si/SiO2/Si3N4) of micro/nanodimensions. We have applied this biosensor for DNA testing and for detection of single nucleotide polymorphisms at BRCA-1 gene, involved in breast cancer development, without target labeling. The oligonucleotide probe is immobilized by covalent attachment to the sensor surface through silanization procedures. The hybridization was performed for different DNA target concentrations showing a lowest detection limit at 10 pM. Additionally, we have detected the hybridization of different concentrations of DNA target with two mismatching bases corresponding to a mutation of the BRCA-1 gene. Following the way of the lab-on-a-chip microsystem, integration with the microfluidics has been achieved by using a novel fabrication method of 3-D embedded microchannels using the polymer SU-8 as structural material. The optofluidic chip shows good performances for biosensing.
Nanomechanical biosensors have emerged as a promising platform for specific biological. Among the advantages are direct detection without need of labelling with fluorescent or radioactive molecules, very high sensitivity, reduced sensor area, and suitability for integration using silicon technology. Here we have studied the immobilization of oligonucleotide monolayers by monitoring the microcantilever bending. Oligonucleotides were derivatized with thiol molecules for self-assembly on the gold-coated side of a microcantilever. The geometry of the binding and the surface density were studied by mixing derivatized oligonucleotides with spacer self-assembled monolayers and by controlling the oligonucleotide functional group form. These results are compared with fluoresencent and chemiluminescence techniques. Furthermore, we present the first results of direct pesticide detection with microcantilever-based biosensors. Herbicide DDT was detected by performing competitive assays, in which the cantilever was coated with a synthetic DDT hapten, and it was exposured to different rations between the monoclonal antibody and the DDT. A new technique is presented for the detection of the nanomechanical response for biosensing applications, in which the resonant frequency is measured with about two orders of magnitude higher sensitivity. The low quality factor of the microcantilever in liquid is increased up by using an active feedback control, in which the cantilever oscillation is amplified and delayed and it is used as a driving force. The technique has been applied for the detection of ethanol, proteins, and pathogens.