A method for preparing a dry nanoparticle-containing specimen in a specimen kit for transmission electron microscope, TEM, observations and/or characterizations of a distribution status of nanoparticles in a liquid sample, comprising: (a) providing a specimen kit adaptable and compatible with a commercial TEM holder, the specimen kit comprising: (i) a top substrate and a bottom substrate, each of the substrates (302, 304) having a top surface and a bottom surface and a length of L1, a width of W1, and a thickness T1 ranging from 50 nm to 300 nm, the top and the bottom substrates (302, 304) being transparent and substantially parallel to each other; (ii) a first spacer and a second spacer, each having a length of L2, a width of W2, and a thickness of h, located beneath the top substrate and sitting on the bottom substrate, the second spacer being positioned opposite to and spaced apart from the first spacer at a distance of d, wherein the width of the spacer (502a, 502b) W2 is smaller than the width of the top substrate W1; and (iii) a non-enclosed chamber having two ends open to the atmosphere and formed between the top and bottom substrates (302, 304) and between the first and second spacers (502a, 502b), being characterized by having a length of L1, a width of d, and a height of h defined by the thickness of the spacer (502a, 502b), wherein the height h is smaller than or equal to 5 μm, the length L1 is no greater than 1 cm, the width d is smaller than 1 cm; (b) loading a liquid sample containing nanoparticles into the chamber; and (c) drying the liquid sample within the non-enclosed chamber to obtain a dry nanoparticle-containing specimen, wherein the nanoparticles are attached onto the bottom surface of the top substrate and the top surface of the bottom substrates. (a) providing a specimen kit adaptable and compatible with a commercial TEM holder, the specimen kit comprising: (i) a top substrate and a bottom substrate, each of the substrates (302, 304) having a top surface and a bottom surface and a length of L1, a width of W1, and a thickness T1 ranging from 50 nm to 300 nm, the top and the bottom substrates (302, 304) being transparent and substantially parallel to each other; (ii) a first spacer and a second spacer, each having a length of L2, a width of W2, and a thickness of h, located beneath the top substrate and sitting on the bottom substrate, the second spacer being positioned opposite to and spaced apart from the first spacer at a distance of d, wherein the width of the spacer (502a, 502b) W2 is smaller than the width of the top substrate W1; and (iii) a non-enclosed chamber having two ends open to the atmosphere and formed between the top and bottom substrates (302, 304) and between the first and second spacers (502a, 502b), being characterized by having a length of L1, a width of d, and a height of h defined by the thickness of the spacer (502a, 502b), wherein the height h is smaller than or equal to 5 μm, the length L1 is no greater than 1 cm, the width d is smaller than 1 cm; (i) a top substrate and a bottom substrate, each of the substrates (302, 304) having a top surface and a bottom surface and a length of L1, a width of W1, and a thickness T1 ranging from 50 nm to 300 nm, the top and the bottom substrates (302, 304) being transparent and substantially parallel to each other; (ii) a first spacer and a second spacer, each having a length of L2, a width of W2, and a thickness of h, located beneath the top substrate and sitting on the bottom substrate, the second spacer being positioned opposite to and spaced apart from the first spacer at a distance of d, wherein the width of the spacer (502a, 502b) W2 is smaller than the width of the top substrate W1; and (iii) a non-enclosed chamber having two ends open to the atmosphere and formed between the top and bottom substrates (302, 304) and between the first and second spacers (502a, 502b), being characterized by having a length of L1, a width of d, and a height of h defined by the thickness of the spacer (502a, 502b), wherein the height h is smaller than or equal to 5 μm, the length L1 is no greater than 1 cm, the width d is smaller than 1 cm; (b) loading a liquid sample containing nanoparticles into the chamber; and (c) drying the liquid sample within the non-enclosed chamber to obtain a dry nanoparticle-containing specimen, wherein the nanoparticles are attached onto the bottom surface of the top substrate and the top surface of the bottom substrates.