Sure, I'd be happy to help you plan your one-day itinerary in Singapore! Here's a suggested itinerary that will allow you to experience some of the best attractions and activities that this vibrant city-state has to offer:

Morning: Start your day with a visit to Gardens by the Bay, a stunning nature park that features towering supertrees, beautiful gardens, and two giant conservatories. You can explore the Flower Dome, which is the world's largest glass greenhouse, and the Cloud Forest, which houses a 35-meter-tall indoor waterfall.

Afternoon: Next, head over to Marina Bay Sands, an iconic hotel and entertainment complex that boasts a rooftop infinity pool with breathtaking views of the city skyline. You can also check out the ArtScience Museum, which features interactive exhibits on art, science, and technology.

Evening: In the evening, take a stroll along the Singapore River and enjoy the city's vibrant nightlife. Clarke Quay is a popular spot for dining and drinking, with plenty of restaurants, bars, and clubs to choose from. Alternatively, you can head to Chinatown for some delicious street food and shopping.

If you have more time, you can also consider visiting other popular attractions such as Sentosa Island, Universal Studios Singapore, or the Merlion Park. Whatever you decide to do, I'm sure you'll have a fantastic time exploring all that Singapore has to offer!