Bladder cancer is a common malignancy with high rates of recurrence and progression. Chemotherapy is employed at various stages of treatment to improve patient outcomes and survival; however, it is sometimes ineffective and often associated with significant side effects. Moreover, growing evidence suggests that chemotherapy may paradoxically enhance tumor invasiveness and metastatic potential in certain cancer types. These concerns underscore the need to better understand the impact of chemotherapy and to develop personalized prognostic strategies for managing bladder cancer. Here, we present an organoid biosensing platform designed to evaluate chemotherapy-induced effects in a patient-specific manner. Freshly isolated tumor organoids and self-assembled microtumors derived from transurethral resection of bladder tumors are cultured within a tumor-on-gel biomimetic microenvironment. By integrating live single cell nanobiosensors with 3D time-lapse microscopy, the platform enables real-time detection of molecular biomarkers and rapid assessment of tumor invasiveness. We demonstrate the platform's capability to evaluate cisplatin-induced invasion in bladder cancer organoids at the individual patient level. These findings highlight the potential of this organoid biosensing system to investigate patient-specific risks of chemotherapy-induced invasion and to guide more personalized approaches to bladder cancer treatment.