[Show abstract][Hide abstract] ABSTRACT: Increasingly, advances in microtechnologies are focused on obtaining new chips intended for applications in fields such as nanomedicine and cell biology, taking advantage of the ability of microelectronics to manufacture devices with cell dimensions and a large variety of features. Here, we report a technology for the fabrication of multi-material chips, using polysilicon and gold as device layers, to be used as bi-functional cell-internalizable devices. In our case, one of the main technological challenges is to overcome the low adherence between these two materials, especially because of their small contact-area, only 9 μm2. Thus, in order to circumvent this difficulty a chromium adherent-layer was deposited in between. After fabrication, the devices following this design can be successfully internalized inside living macrophages without affecting their viability. The advantage of having multiple material layers in one device is the potential to render multi-tasking chips, as once they are appropriately functionalized, we can provide the chip the ability of being multi-functional. Hence, and as a proof of concept, two different proteins, Wheat Germ Agglutinin (WGA) and Concanavalin (ConA), were immobilized on the chip surface through self-assembled monolayers using orthogonal chemistry. The results of this work show a well-controlled fabrication, the bi-functional capabilities and no cell-toxicity of intracellular polysilicon–chromium–gold chips. Eventually, two different dyes (Oregon Green® 488 and BODIPY® 581/591) were used to bi-functionalize each surface of the multi-material chip in order to demonstrate that functional chips can also be internalized in living cells. These devices have a promising future as intracellular functional platforms for biosensing, drug delivery and diagnosis.
Sensors and Actuators B Chemical 03/2015; 209:212-224. DOI:10.1016/j.snb.2014.11.077 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Magnetically-actuable, polymer-based variable optical attenuators (VOA) are presented in this paper. The design comprises a cantilever which also plays the role of a waveguide and the input/output alignment elements for simple alignment, yet still rendering an efficient coupling. Magnetic properties have been conferred to these micro-opto-electromechanical systems (MOEMS) by implementing two different strategies: in the first case, a magnetic sensitive stimuli material (M-SSM) is obtained by a combination of polydimethylsiloxane (PDMS) and ferrofluid (FF) in ratios between 14.9 wt % and 29.9 wt %. An M-SSM strip under the waveguide-cantilever, defined with soft lithography (SLT), provides the required actuation capability. In the second case, specific volumes of FF are dispensed at the end of the cantilever tip (outside the waveguide) by means of inkjet printing (IJP), obtaining the required magnetic response while holding the optical transparency of the waveguide-cantilever. In the absence of a magnetic field, the waveguide-cantilever is aligned with the output fiber optics and thus the intrinsic optical losses can be obtained. Numerical simulations, validated experimentally, have shown that, for any cantilever length, the VOAs defined by IJP present lower intrinsic optical losses than their SLT counterparts. Under an applied magnetic field (Bapp), both VOA configurations experience a misalignment between the waveguide-cantilever and the output fiber optics. Thus, the proposed VOAs modulate the output power as a function of the cantilever displacement, which is proportional to Bapp. The experimental results for the three different waveguide-cantilever lengths and six different FF concentrations (three per technology) show maximum deflections of 220 µm at 29.9 wt % of FF for VOASLT and 250 µm at 22.3 wt % FF for VOAIJP, at 0.57 kG for both. These deflections provide maximum actuation losses of 16.1 dB and 18.9 dB for the VOASLT and VOAIJP, respectively.
Journal of Micromechanics and Microengineering 12/2014; 24(12). DOI:10.1088/0960-1317/24/12/125008 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports and compares the implementation of magnetic variable optical attenuators (M-VOA) by two fabrication strategies. In the first case, a two-layer structure containing a non-doped polydimethylsiloxane (PDMS) layer on a magnetic PDMS (M-PDMS) layer is fabricated by soft lithography (SLT). M-PDMS is obtained by doping PDMS with different ferrofluid (FF) volumes. The second technology consists of selectively dispense FF microdroplets using the inkjet printing technique (IJP) on a non-doped, non-cured PDMS structure, previously defined by SLT. In this second case, FF volumes are encapsulated inside the polymer matrix. The optical and mechanical properties of structures fabricated using both strategies and containing similar ferrofluid amounts are compared.
Sensors and Actuators A Physical 08/2014; 215. DOI:10.1016/j.sna.2014.01.021 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports the implementation of magnetic variable optical attenuators (M-VOA) by soft lithography (SLT) and using polydimethylsiloxane (PDMS) as constituent material. Two different fabrication protocols are used and compared. In the first case, a two-layer structure containing a clean PDMS layer on a magnetic PDMS (M-PDMS) layer is fabricated by SLT. M-PDMS is obtained by doping clean PDMS with different ferrofluid (FF) amounts. The second protocol consists of selectively dispensing droplets of FF by the inkjet printing technique (IPT) on a clean and non-cured PDMS structure previously defined by SLT. The optical and mechanical properties of structures fabricated using both protocols and containing similar ferrofluid amounts are compared.
Micro Electro Mechanical Systems (MEMS), 2013 IEEE 26th International Conference on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The low number of oocytes collected from unstimulated donors by ovum pick-up means that embryos produced from each female have to be cultured in very small groups. Because embryo quality and development rates are reduced in individual and small group culture, several methods to culture embryos individually but sharing the same medium have been designed. However, these systems prevent embryo movements, interfering with paracrine factors transmission and gradient changes. Here, we present an alternative in vitro culture method to allow the co-culture of embryos from different origins, without movement restriction and preserving their pedigree, by labelling the zygotes with polysilicon barcodes attached to the outer surface of the zona pellucida (ZP). Barcodes (10×6×1µm) with 8 rectangular bits of binary codification (256 possible combinations), which can be read under a standard inverted microscope, were fabricated using silicon microtechnologies. To provide the barcodes with a ZP-binding capacity, they were biofunctionalized by self-assembled monolayers with the wheat germ agglutinin (WGA) lectin, which recognizes specific saccharides highly abundant in the ZP of most mammalian species. As a proof of concept, the culture method was tested on bovine zygotes produced from slaughterhouse-derived cow oocytes matured and fertilized in vitro. Using a mouth-controlled pipette, presumptive zygotes were individually rolled over WGA-biofunctionalized barcodes (8 barcodes/embryo) previously placed at the bottom of a drop of manipulation media. Four different barcodes, each one with a different codification, were used to encode 25 embryos (6-7 embryos/barcode codification), which were then cultured together in the same drop of medium. Day 7 (D7) and Day 8 (D8) blastocyst, and barcode retention rates were assessed. In addition, D7 expanded blastocysts were vitrified by the cryotop method and post-warming survival was determined as re-expansion rate at 24h in culture. Finally, the quality of D8 blastocysts was assessed by differential staining and counting of inner cell mass (ICM) and trophectoderm (TE) cells. In all the experiments, a control group without barcodes was cultured and vitrified-warmed. Data were analyzed by chi-square and Mann-Whitney tests. The presence of barcodes attached to the ZP did not affect in vitro embryo development (D8 blastocysts: 29.7% control n=309, 36.2% encoded n=315), post-warming survival (86.4% control n=66, 80.5% encoded n=82), or blastocyst quality (IMC/TE: 22.1±1.4/64.5±5.7 control n=18, 22.2±1.7/64.1±6.1 encoded n=23). The labelling system was effective until D8 of culture, as all the embryos maintained barcodes attached (4±1.8 barcodes/embryo) and could be identified, even after undergoing vitrification and warming. In conclusion, identification of co-cultured embryos by biofunctionalized barcodes attached to the ZP is feasible and will allow to culture embryos from different donors in the same drop, keeping the benefits of collective culture.
[Show abstract][Hide abstract] ABSTRACT: This paper describes a technique that uses applied force to dice anodically bonded silicon–glass wafers with high yields. The chips are suspended to the wafer by anchors; when pressure is applied to a chip, stress concentrates at the narrow anchors, which then fracture and release the chip from the wafer. Anchor fracturing has been used to dice crystalline and non-crystalline materials but its application to dicing constructs of various materials has remained challenging because of the disparity with which fractures propagate in different materials and in their interfaces. The technique we present here makes it possible to fracture composite materials (silicon and glass anodically bonded) by eliminating any material interface from the fracturing regions—i.e. the anchors. The approach was tested using two types of anchors fabricated in anodically bonded silicon–glass wafers: in one type, the silicon–glass interface expanded most of the anchor (coincident anchors) but such an interface was inexistent in the other type (non-coincident anchors). The study determined dicing yields—i.e. percentage of chips not damaged by the fracture of the anchors—of ~40% and 100% for test structures with coincident and non-coincident anchors, respectively. The presence of a silicon–glass interface in the suspending anchors often resulted in fractures propagating away from the anchors, and ultimately in damage to the suspended chips. This technique provides an inexpensive, robust and simple alternative to currently available dicing methods for the glass–silicon wafer pairs frequently used in wafer-level packaging of MEMS.
Journal of Micromechanics and Microengineering 01/2012; 22(2):025023. DOI:10.1088/0960-1317/22/2/025023 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on a new approach for magnetic imaging, highly sensitive even in the presence of external, strong magnetic fields. Based on FIB-assisted fabricated high-aspect-ratio rare-earth nanomagnets, we produce groundbreaking magnetic force tips with hard magnetic character where we combine a high aspect ratio (shape anisotropy) together with strong crystalline anisotropy (rare-earth-based alloys). Rare-earth hard nanomagnets are then FIB-integrated to silicon microcantilevers as highly sharpened tips for high-field magnetic imaging applications. Force resolution and domain reversing and recovery capabilities are at least one order of magnitude better than for conventional magnetic tips. This work opens new, pioneering research fields on the surface magnetization process of nanostructures based either on relatively hard magnetic materials-used in magnetic storage media-or on materials like superparamagnetic particles, ferro/antiferromagnetic structures or paramagnetic materials.
[Show abstract][Hide abstract] ABSTRACT: In this work, two types of polycrystalline silicon (polysilicon) microparticles were modified with specific ligands in order to be selectively attached to chemical residues located at the plasma membrane and thus to be applied to study individual cells in culture. Two different functionalization approaches based on adsorption and covalent attachment were assayed. A comparative study of the efficiency of the ligand immobilization and stability of the modified particle in the culture medium was carried out using the selected ligands labeled with a fluorophore. Cylindrical microparticles (nonencoded microparticles) and shape-encoded microparticles (bar codes) were used with the aim of demonstrating the nondependence of the particle size and shape on the efficiency of the immobilization protocol. Fluorescence imaging and statistical analysis of the recorded fluorescence intensity showed that the covalent attachment of the ligand to the surface of the microparticle, previously modified with an aldehyde-terminated silane, gave the best results. As a proof of concept, Vero cells in culture were labeled with the covalently modified bar codes and successfully tracked for up to 1 week without observing any alteration in the viability of the cells. Bar code numbers could be easily read by eye using a bright-field optical microscope. It is anticipated that such modified microparticles could be feasible platforms for the introduction of other analytical functions of interest in single-cell monitoring and cell sorting in automatic analysis systems.
[Show abstract][Hide abstract] ABSTRACT: This paper focuses on the design and experimental test of a null-offset differential electromagnetic sensor characterized by simplicity, flexibility and low cost. This sensor consists of two planar excitation coils, which generate magnetic field and a planar acquisition coil, which senses the sample material. The differential configuration of the sensor improves signal conditioning and reduces the common-mode noise. We present analytical and numerical (simulation) studies of the working principle. Experiments were performed to test the ability of the sensor to detect non-invasively: (i) the presence of metallic samples and (ii) the variations of glucose in human blood.
Sensors and Actuators A Physical 11/2010; 164(1-2-164):15-21. DOI:10.1016/j.sna.2010.09.008 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. As expected, a square root dependence has been found for in-plane forces. Nevertheless, the problem is more complex when out-of plane forces are considered. Out-of-plane forces gives rise to an initial quadratic dependence which turns into a square root dependence from a certain stress value. The quadratic range increases and the rate of change of the frequency decreases as the surface of the magnet fixed on the membrane increases. The study has addressed these problems and both, experimental and simulated results have been compared and a good agreement between experimental and simulated results has been found Comment: 14 pages, 10 figures
Sensors and Actuators A Physical 08/2010; 163(1). DOI:10.1016/j.sna.2010.07.012 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A system of two solid microlenses with uncoupled optical properties is presented. This structure has been designed in order to have one lens as a reference, while the other one can be mechanically tuneable. The reference lens presents a diameter of 2 μm and it is placed in the optical axis of the mechanically tuneable lens, which has a diameter of 10 μm. The proposed microoptical structure has been fabricated in poly(dimethilsiloxane) (PDMS) merging deep reactive ion etching, SU-8 and soft lithography, with a low-cost (mass-production), simple and highly repetitive technology. This device was numerically simulated prior to its fabrication, to optimize its design and improve its behaviour. In addition, an optical characterization of the fabricated devices was carried out. Both simulation and experimental results shows a good agreement, under mechanical actuation behaviour of the reference lens is invariable, while the tuneable lens become an elliptic lens and the interval of Sturm can be observed. These results provide a proof of concept of the proposed devices and validate both the design and the fabrication technology.
[Show abstract][Hide abstract] ABSTRACT: Design, fabrication and testing of a novel micromachined “quasi-digital” microflow regulator for integrated microfluidic systems. Operation relies on the use of a permanent magnet which interacts with an electrodeposited layer of Co–Ni on an array of V-shaped cantilever beams under a constant pressure. Each valve actuates as an on–off fluidic switch, opening or closing its corresponding microchannel. The flow can be adjusted to a set of different values (digital) by changing the position of the magnet. The microflow regulator has been designed, fabricated and experimentally tested showing a flow variation of 211% at a pressure of 160mbar.
Sensors and Actuators A Physical 07/2010; 162(1):107-115. DOI:10.1016/j.sna.2010.04.025 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel, versatile and robust technology to manufacture transparent micropipettes, suitable for biological applications, is presented here. Up to three deep reactive ion etchings have been included in the manufacturing process, providing highly controlled geometry of reservoirs, connection cavities and inlet ports. Etching processes have been used for the definition of chip and reservoir and for nozzle release. Additionally, special design considerations have been developed to facilitate micro-to-macro fluidic connections. Implementation of anodic bonding to seal a glass substrate to the fluidic structure etched on Si, allowed observation of the flow inside the reservoir. Flow tests have been conducted by filling channels with different fluids. Flow was observed under an optical microscope, both during capillary filling and also during pumping. Dispensing has been demonstrated by functionalizing the surface of an AFM cantilever. Mechanical tests performed by piercing live mouse cells with FIB-sharpened micropipettes suggest the design is sturdy for biological piercing applications.
Journal of Micromechanics and Microengineering 09/2009; 19(10):105013. DOI:10.1088/0960-1317/19/10/105013 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Packaging technologies are a great issue in MEMS/NEMS fabrication. Moreover, silicon to glass anodic bonding is a common boding technique for MEMS/NEMS packaging. Hence, dicing the wafer into individual devices is a real challenge for fragile structures. This investigation shows an extension of the manual cleaving dicing for bonded silicon/glass wafers. The designed structure with no coincident anchors between silicon and glass avoids that the fracture expands toward the interior of the device during manual cleaving. Highest stresses are localized on the anchors, causing the fracture in those points. This method was experimentally tested to dice anodically bonded silicon-glass wafers.
[Show abstract][Hide abstract] ABSTRACT: In this paper it is shown the design and characterization of a differential electromagnetic sensor. In absence of the sample the output signal of the sensor is null. There will only be an output signal in the presence of a magnetic material or a conductive sample in which eddy currents are generated, producing an external magnetic field. This working principle is non invasive and improves greatly the possibilities for signal conditioning. The sensor has been tested with a copper sample and for detection of variations in the blood glucose concentration, showing high sensitivity and potentialities for other applications.
[Show abstract][Hide abstract] ABSTRACT: Microworld barcoding has become a promising tool for cell biology. Individual and subpopulation cell tracking is of great interest to evaluate cell behaviour. Nowadays, many micrometer and even nanometer size silicon structures can be fabricated using microelectronics techniques. In this work we report for first time the development of 3D barcodes based on silicon substrate. The proposed silicon micromachining technology based on deep reactive ion etching (DRIE) allows to obtain micrometer-sized cylindrical structures with vertical etch profile that defines a bit = 1 and non-vertical etch profile that defines a bit = 0. Although this technology will allow more than 15 bits representation, only 4–8 bits are necessary for cell labelling. The results of this work show that DRIE has become a versatile technique to produce high aspect 3D biocompatible silicon-based barcodes structures for cell studies.
[Show abstract][Hide abstract] ABSTRACT: In this work a magnetic field gradiometer device has been developed. This device is not composed by two sensors separated a certain distance but by a single-sensor device which measures the real gradient value just at the point where it is wanted to be measured. The experimental set-up consists of a sensor head (a membrane with a fixed permanent magnet on it) vibrating at its resonance frequency, due to an alternating magnetic field gradient. Detection is performed using an optoelectronic method. Two different measurement techniques have been used: frequency measurements (the resonance frequency is measured for every external magnetic field gradient value) and amplitude measurements (the signal amplitude is measured without changing the resonance frequency obtained without an external magnetic field gradient applied). The mechanical stresses of the membrane are related with the dependence of both magnitudes (frequency and amplitude) on the external magnetic field gradient. The minimum and maximum value of the resonance frequency and signal amplitude respectively, correspond with magnetic forces equal to the magnet weight of the sensor head. This prototype shows a noise-limited sensitivity of 2 Gauss/m/√Hz at zero gradient. This device could be used also as a magnetic susceptometer.
[Show abstract][Hide abstract] ABSTRACT: Micromachining techniques are proposed to mass-manufacture innovative silicon oxide micropipettes and conventional boron-silicate pipettes with highly customized tips to address increasingly demanding cell handling procedures. Cell handling has become a crucial procedure in cell biology, especially in nuclear transfer, DNA injection, and in assisted reproductive techniques. Most pipette manufacturing procedures involve tedious artisanal methods prone to failure and with limited functionality. We expect high tip customization to have a large impact in current and future cell manipulation, paving the way for augmented functionality. Although proper biocompatibility assessments remain to be explored, initial pierced embryos are seen to continue their division procedure up to at least 24 hours. The continued cellular division is a good sign of biocompatibility. These results suggest that residual chemical agents or gallium ions injected during milling could be harmless to life development. We conclude that we have produced a novel technique combining microfabrication and Focus Ion Beam processes with great potential for industrial applications.
Proceedings of SPIE - The International Society for Optical Engineering 05/2009; DOI:10.1117/12.820667 · 0.20 Impact Factor