## 1 Introduction  
The ultrastructure of biological specimens is usually examined using transmission electron microscopy (TEM). To obtain high-resolution images of the ultrastructure, traditional TEM requires several complicated steps, including sample fixation, dehydration, infiltration, embedding, ultrathinsectioning, and staining [1]. If one of these steps is not done well, the ultrastructural image may show many artifacts. Therefore, it takes a lot of time and high-level techniques to observe the ultrastructure of biological samples using traditional TEM. In addition, because most biological specimens are soft and rich in water, samples need to be fixed, dehydrated, infiltrated, and embedded with many chemicals before ultrathin sectioning can be performed. These chemicals likely affect the original ultrastructure [2]. Therefore, many morphologists are actively looking for faster and more effective materials and methods to observe nanoscale biological samples without affecting their ultrastructure. [PERSON] et al. [3] developed a microchip (called the K-kit), which can directly observe nanoparticles in an aqueous solution, providing an impressive method to observe the ultrastructure of biological specimens. This microchip contains a sample chamber, which consists of SiO\({}_{2}\) nanomembranes with an observation window. Specimens in aqueous solution can be loaded into the chamber and then examined by an electron microscope. Previously, images of non-biological particles and living bacteria were successfully demonstrated with this microchip [3; 4; 5]. Sample preparation steps of this microchip are simpler and faster than those of traditional TEM. In addition, no chemicals are required for fixation, dehydration, infiltration, or embedding, so biological specimens can be kept in their native state. Although the microchip was used to quantify nanoparticles in plasma [6], it still has not been confirmed whether granules of living human platelets in an aqueous solution can be examined with this microchip. In this study, we performed negative staining and immunoelectron microscopy to quickly identify specific granules of human platelets using this microchip. Platelets are small, anucleated blood cells that execute many important functions in the clotting of blood under physiological and pathological conditions. They play an initial role in maintaining the integrity of blood vessels and are the first line of defense against hemorrhaging by forming a thrombus. The coagulation cascade is initiated by thrombin production induced by activation of platelets and release of granules [7; 8]. Functional roles of platelets have expanded in recent years to include processes such as inflammation, innate immunity, growth and development, angiogenesis, wound healing, and cancer metastasis [9; 10; 11]. The exocytosis of platelet granules is important to platelet function and participates in platelet activities [12]. Platelets contain at least three major types of granules: \(\alpha\)-granules, dense granules, and lysosomes. These different membrane-bound granules contain specific mediators and molecules and create various functions of platelets [13; 14]. \(\alpha\)-Granules are the most abundant granules and the major protein storage compartment in platelets. They contain some membrane-associated receptors (for example, P-selectin) and several soluble substances (for example, platelet factor 4, fibrinogen, thrombospondin, platelet-derived growth factor, etc.) [15; 16]. Exocytosis of \(\alpha\)-granules is evaluated primarily through plasma membrane expression of P-selectin as assessed by flow cytometry or estimating the release of granule substances [17]. More recent work using serial block face-scanning electron microscopy for a 3D ultrastructural analysis showed that \(\alpha\)-granules in resting human platelets are ovoid with a generally homogeneous matrix [18]. Several studies explored homogeneity in the size, shape, and composition of \(\alpha\)-granules [19; 20; 21].