There is provided a method for producing a silica sol including: a first step of adding an organic acid to at least one of liquid (A) containing an alkaline catalyst, water, and a first organic solvent and liquid (C) containing water; and a second step of mixing the liquid (A) with liquid (B) containing an alkoxysilane or its condensate and a second organic solvent, and the liquid (C) to make a reaction liquid after the first step.

Embodiments described herein may be useful in the detection of analytes. The systems and methods may allow for a relatively simple and rapid way for detecting analytes such as chemical and/or biological analytes and may be useful in numerous applications including sensing, food manufacturing, medical diagnostics, performance materials, dynamic lenses, water monitoring, environmental monitoring, detection of proteins, detection of DNA, among other applications. For example, the systems and methods described herein may be used for determining the presence of a contaminant such as bacteria (e.g., detecting pathogenic bacteria in food and water samples which helps to prevent widespread infection, illness, and even death). Advantageously, the systems and methods described herein may not have the drawbacks in current detection technologies including, for example, relatively high costs, long enrichment steps and analysis times, and/or the need for extensive user training. Another advantageous feature provided by the systems and methods described herein includes fabrication in a relatively large scale. In some embodiments, the systems and methods may be used in conjunction with a detector including handheld detectors incorporated with, for example, smartphones (e.g., for the on-site detection of analytes such as pathogenic bacteria).

The aminosilane-modified colloidal silica dispersion contains colloidal silica particles having surfaces to which there are bound a first silyl group represented by the following formula (1): R.sup.1.sub.aSi(OR.sup.2).sub.3-aO and a second silyl group represented by the following formula (2): R.sup.3.sub.bSi(OR.sup.4).sub.3-bO and, as a dispersion medium, a mixed solvent formed of a polar solvent S1 having a dielectric constant at 20 C. of 15 or higher and lower than 60 and a non-polar solvent S2 having a dielectric constant at 20 C. of 1 or higher and lower than 15, at a mass ratio (S1/S2) of 0.3 to 6.

The aminosilane-modified colloidal silica dispersion contains colloidal silica particles having surfaces to which there are bound a first silyl group represented by the following formula (1): R.sup.1.sub.aSi(OR.sup.2).sub.3-aO and a second silyl group represented by the following formula (2): R.sup.3.sub.bSi(OR.sup.4).sub.3-bO and, as a dispersion medium, a mixed solvent formed of a polar solvent S1 having a dielectric constant at 20 C. of 15 or higher and lower than 60 and a non-polar solvent S2 having a dielectric constant at 20 C. of 1 or higher and lower than 15, at a mass ratio (S1/S2) of 0.3 to 6.

Composite oxide fine particles are produced by sol-gel method under conditions in which coarse particles and aggregated particles are unlikely to be generated, and the composite oxide fine particles are further wet-filtered using a filter to remove the coarse particles and the aggregated particles. Then, a salt is added to a dispersion of the composite oxide fine particles to produce weak aggregates of the composite oxide fine particles in the dispersion. A solid content is separated from the dispersion of the composite oxide fine particles containing the aggregates, and then dried. The solid content is easily made finer because no firm aggregates are generated during the drying. That is, composite oxide fine particles containing no coarse particles and aggregated particles are obtained. Use of a known cracking means can further reduce the amount of coarse particles.

A method for producing a silica sol containing a small amount of metal impurities and in which colloidal silica having an elongated particle shape dispersed in a solvent, includes: preparing a raw material liquid by adding a compound as an anion source selected from inorganic acids, organic acids, and their ammonium salts, and ammonia to a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 1 to 6% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 3.0 to 7.0%; and heating the raw material liquid at 80 to 200 C. for 0.5 to 20 hours. The elongated colloidal silica particles exhibit a D.sub.L/D.sub.B ratio of 2.5 or more. D.sub.L is an average particle diameter as measured by the dynamic light scattering method. D.sub.B is a primary particle diameter as measured by the nitrogen gas adsorption method.

A method for producing a silica sol containing a small amount of metal impurities and in which colloidal silica having an elongated particle shape dispersed in a solvent, includes: preparing a raw material liquid by adding a compound as an anion source selected from inorganic acids, organic acids, and their ammonium salts, and ammonia to a colloidal aqueous solution of activated silica having an SiO.sub.2 concentration of 1 to 6% by mass and a pH of 2 to 5 so that the mass ratio of the compound to SiO.sub.2 is 3.0 to 7.0%; and heating the raw material liquid at 80 to 200 C. for 0.5 to 20 hours. The elongated colloidal silica particles exhibit a D.sub.L/D.sub.B ratio of 2.5 or more. D.sub.L is an average particle diameter as measured by the dynamic light scattering method. D.sub.B is a primary particle diameter as measured by the nitrogen gas adsorption method.

A method for producing an acrylic resin-coated silica particle dispersion by (1), mixing and heating silica particles (A), an organic solvent (B) and a monomer having a polymerizable unsaturated group and a hydrolyzable silyl group (C) to obtain a polymerizable unsaturated group-containing silica particle dispersion (i), (2) adding a tertiary amine (D) with a molecular weight of 120 to 380 and having a terminal alkyl and/or aryl group, to the component (i) dispersion, to obtain a polymerizable unsaturated group-containing silica particle dispersion (ii), and (3) reacting the component (ii) dispersion with a polymerizable unsaturated monomer (E), in a solid mass ratio of (ii):(E)=20:80 to 90:10, to obtain an acrylic resin-coated silica particle dispersion.

A method for producing an acrylic resin-coated silica particle dispersion by (1), mixing and heating silica particles (A), an organic solvent (B) and a monomer having a polymerizable unsaturated group and a hydrolyzable silyl group (C) to obtain a polymerizable unsaturated group-containing silica particle dispersion (i), (2) adding a tertiary amine (D) with a molecular weight of 120 to 380 and having a terminal alkyl and/or aryl group, to the component (i) dispersion, to obtain a polymerizable unsaturated group-containing silica particle dispersion (ii), and (3) reacting the component (ii) dispersion with a polymerizable unsaturated monomer (E), in a solid mass ratio of (ii):(E)=20:80 to 90:10, to obtain an acrylic resin-coated silica particle dispersion.

Provided is a method for producing a silica sol. A gel-like material cannot be generated and highly associated silica particles can be obtained.

A method for producing a silica sol, comprising a step of making a reaction liquid by mixing liquid (A) comprising an alkaline catalyst, water, a first organic solvent and silica particles for association with liquid (B) comprising at least one of tetramethoxysilane and a condensate thereof and a second organic solvent, wherein during the mixing, an addition rate of the liquid (B) is 8.510.sup.4 to 5.610.sup.3 mol/min in terms of silicon atoms with respect to 1 mol of the water contained in the liquid (A).