We report experimental results of label-free anti-bovine serum albumin (anti-BSA) antibody detection using a SOI planar photonic crystal waveguide previously bio-functionalized with complementary BSA antigen probes. Sharp fringes appearing in the slow-light regime near the edge of the guided band are used to perform the sensing. We have modeled the presence of these band edge fringes and demonstrated the possibility of using them for sensing purposes by performing refractive index variations detection, achieving a sensitivity of 174.8 nm/RIU. Then, label-free anti-BSA biosensing experiments have been carried out, estimating a surface mass density detection limit below 2.1 pg/mm2 and a total mass detection limit below 0.2 fg.

We report an experimental demonstration of single-strand DNA (ssDNA) detection at room temperature using a photonic-crystal-waveguide-based optical sensor. The sensor surface was previously biofunctionalized with ssDNA probes to be used as specific target receptors. Our experiments showed that it is possible to detect these hybridization events using planar photonic-crystal structures, reaching an estimated detection limit as low as 19.8 nM for the detection of the complementary DNA strand.

Methodology for the functionalization of silicon-based materials employed for the development of photonic label-free nanobiosensors is reported. The studied functionalization based on organosilane chemistry allowed the direct attachment of biomolecules in a single step, maintaining their bioavailability. Using this immobilization approach in probe microarrays, successful specific detection of bacterial DNA is achieved, reaching hybridization sensitivities of 10 pM. The utility of the immobilization approach for the functionalization of label-free nanobiosensors based on photonic crystals and ring resonators was demonstrated using bovine serum albumin (BSA)/anti-BSA as a model system.

A technique for the development of low-cost and high-sensitivity photonic biosensing devices is proposed and experimentally demonstrated. In this technique, a photonic bandgap structure is used as transducer, but its readout is performed by simply using a broadband source, an optical filter, and a power meter, without the need of obtaining the transmission spectrum of the structure; thus, a really low-cost system and real-time results are achieved. Experimental results show that it is possible to detect very low refractive index variations, achieving a detection limit below 2 × 10 −6 refractive index units using this low-cost measuring technique. , even became commercially available some years ago, devices based on integrated planar photonic structures are envisaged as a highly promising alternative for future lab-ona-chip (LoC) devices. This is due to several advantages they present compared to previously mentioned sensing technologies, such as compactness, the possibility for multianalyte detection, high sensitivity, high interaction between optical field and target analytes, shorter detection time, label-free detection, and the requirement of very low volumes to perform the sensing. Moreover, the possibility of using mass manufacturing complementary metal-oxide semiconductor techniques allows VLSI of the final devices, which results in a drastic reduction of their cost. Planar photonic sensing devices, which have been most used in the past few years, base their detection on the direct measurement of the shift of the structure's spectral response, as it occurs for ring resonators [4][5][6] or photonic crystals [7][8][9][10]. Therefore, these systems require the use of either a tunable laser source or an optical spectrum analyzer (OSA) to perform the readout of the device, making the total cost of the system significant. Moreover, sweeping times of the order of several seconds up to minutes are needed to acquire each spectrum, preventing an instantaneous observation of the interactions of the target analyte with the sensor. Other photonic structures, such as directional couplers [11] or Mach-Zehnder interferometers (MZIs) [12], which do not require tunable elements in the readout system and would thus allow a reduction in the final cost of the system, have also been proposed. However, compared to ring resonators or photonic crystals, these structures require much larger lengths in order to have enough interaction between the optical field and the target analyte, so that their integration level is limited (note that more compact designs for MZI-based sensors have been proposed [13]).In this Letter, we propose and experimentally demonstrate a new technique for the development of real-time and low-cost integrated photonic sensing devices. The sensing technique is based on using photonic bandgap (PBG) structures to perform the detection, but the PBG shift is indirectly determined by using a filtered broadband optical source as excitation instead of a tunable laser and a power meter at the output, thus significantly...

A proper antibody immobilization on a biosensor is a crucial step in order to obtain a high sensitivity to be able to detect low target analyte concentrations. In this paper, we present an experimental study of the immobilization process of antibodies as bioreceptors on a photonic ring resonator sensor. A protein A intermediate layer was created on the sensor surface in order to obtain an oriented immobilization of the antibodies, which enhances the interaction with the target antigens to be detected. The anti-bovine serum albumin (antiBSA)-bovine serum albumin (BSA) pair was used as a model for our study. An opto-fluidic setup was developed in order to flow the different reagents and, simultaneously, to monitor in real-time the spectral response of the photonic sensing structure. The antiBSA immobilization and the BSA detection, their repeatability, and specificity were studied in different conditions of the sensor surface. Finally, an experimental limit of detection for BSA recognition of only 1 ng/mL was obtained.